The Project Gutenberg eBook of Photographic investigations of faint nebulae This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online at www.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook. Title: Photographic investigations of faint nebulae Author: Edwin Hubble Release date: September 15, 2023 [eBook #71654] Language: English Original publication: Chicago: The University of Chicago Press Credits: Charlene Taylor, Bryan Ness and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.) *** START OF THE PROJECT GUTENBERG EBOOK PHOTOGRAPHIC INVESTIGATIONS OF FAINT NEBULAE *** Transcriber’s Notes: Underscores “_” before and after a word or phrase indicate _italics_ in the original text. Equal signs “=” before and after a word or phrase indicate =bold= in the original text. Illustrations and tables have been moved so they do not break up paragraphs. Small capitals have been converted to SOLID capitals. Typographical and punctuation errors have been silently corrected. PHOTOGRAPHIC INVESTIGATIONS OF FAINT NEBULAE THE UNIVERSITY OF CHICAGO PRESS CHICAGO, ILLINOIS THE BAKER & TAYLOR COMPANY NEW YORK THE CAMBRIDGE UNIVERSITY PRESS LONDON THE MARUZEN-KABUSHIKI-KAISHA TOKYO, OSAKA, KYOTO, FUKUOKA, BOMBAY THE MISSION BOOK COMPANY SHANGHAI The University of Chicago PUBLICATIONS OF THE YERKES OBSERVATORY VOLUME IV PART II PHOTOGRAPHIC INVESTIGATIONS OF FAINT NEBULAE BY EDWIN P. HUBBLE [Illustration] THE UNIVERSITY OF CHICAGO PRESS CHICAGO, ILLINOIS COPYRIGHT 1920 BY THE UNIVERSITY OF CHICAGO All Rights Reserved Published January 1920 Composed and Printed By The University of Chicago Press Chicago, Illinois. U.S.A. PHOTOGRAPHIC INVESTIGATIONS OF FAINT NEBULAE[1] BY EDWIN P. HUBBLE The study of nebulae is essentially a photographic problem for cameras of wide angle and reflectors of large focal ratio. The photographic plate presents a definite and permanent record beside which visual observations lose most of their significance. Perhaps the one field left for the older method is the measurement of sharp nuclei deeply enshrouded in nebulosity. New nebulae are now but rarely seen in the sky, although an hour’s exposure made at random with a large reflector has more than an even chance of adding several small faint objects to the rapidly growing list of those already known. About 17,000 have already been catalogued, and the estimates of those within reach of existing instruments, based on the ratio of those previously known to those new in various fields, lie around 150,000. [1] A dissertation submitted to the Faculty of the Ogden Graduate School of Science of the University of Chicago in candidacy for the degree of Doctor of Philosophy. Extremely little is known of the nature of nebulae, and no significant classification has yet been suggested; not even a precise definition has been formulated. The essential features are that they are situated outside our solar system, that they present sensible surfaces, and that they should be unresolved into separate stars. Even then an exception must be granted for possible gaseous nebulae which appear stellar in the telescope, but whose true nature is revealed by the spectroscope. It may well be that they differ in kind and do not form a unidirectional sequence of evolution. Some at least of the great diffuse nebulosities, connected as they are with even naked-eye stars, lie within our stellar system; while others, the great spirals, with their enormous radial velocities and insensible proper motions, apparently lie outside our system. The planetaries, gaseous but well defined, are probably within our sidereal system, but at vast distances from the earth. In addition to these classes are the numberless small, faint nebulae, vague markings on the photographic plate, whose very forms are indistinct. They may give gaseous spectra, or continuous; they may be planetaries or spirals, or they may belong to a different class entirely. They may even be clusters and not nebulae at all. These questions await their answers for instruments more powerful than those we now possess. Our present hope is to study them statistically, but until motions, either radial or transverse, have been detected we must content ourselves with the problem of their distribution. The first step is to make a systematic survey with powerful telescopes. Fath made a beginning by photographing each of the Kapteyn fields within reach of the Mount Wilson 60-inch reflector with uniform exposures of one hour. He discovered more than eight hundred new nebulae, and confirmed the fact that the small nebulae avoid the Milky Way. This last is vital in its bearing on the question of whether or not these objects belong to our system. A survey with long exposures suggests itself, analogous to that of Kapteyn, but based on the Milky Way rather than on the equator. The writer attempted such a program with the Yerkes 24-inch reflector, giving two-hour exposures. Little progress was made, but one fact stood out, namely, that in the fields of galactic latitude -60° nebulae were very scarce when compared to the numbers met with in galactic latitude +60°. The tendency of small nebulae to gather in clusters has been known for some time. Stratonoff’s map of the distribution of faint nebulae in the Northern Hemisphere shows it very plainly. Max Wolf’s more detailed study of the ecliptic regions with the 16-inch Bruce camera and the 30-inch reflector demonstrates that within these larger regions of the sky where nebulae tend to congregate there are points of accumulation about which the clustering is more marked. He measured the positions of more than four thousand new nebulae, and devised a classification which, while admittedly formal, offers an excellent scheme for temporary filing until a significant system shall be constructed. The present paper has to do with certain clusters of small, faint nebulae which the writer found during the years 1914 to 1916 while photographing with the 24-inch reflector of the Yerkes Observatory. From about 1000 uncatalogued objects, 512 in 7 well-defined clusters were chosen for measurement. Known nebulae in the clusters numbered 76; hence there were, in all, some 588 objects, or an average of 84 per cluster. The fields are as given in Table I. The problem of measuring and reducing accurate positions of objects at a considerable distance from the center of plates taken with a reflector of so large a focal ratio, 1:4, presented serious difficulties. The area covered by each plate is a square of some 110´ to the side. With the full aperture the stellar images are sensibly round only within 5′ of the optical center of the plate. From there outward the coma becomes more and more prominent, distorting the images first into an oval, and finally, near the edge of the plate, into the shape of an arrow, while the point about which the images build up becomes more and more eccentric. For images of various sizes this point will be at various distances from the centers of figure, and at 40′ from the center will fall very nearly at the point of the arrow. This introduces at once an overwhelming magnitude-error, masking whatever distortion of the field may exist. TABLE I =======+==============================+===================== | CENTER (1875.0) | NUMBER FIELD +--------------------+---------+-------+-----+------- | α | δ | Known | New | Total -------+--------------------+---------+-------+-----+------- I | 1ʰ 0ᵐ 30ˢ | +31°44′ | 21 | 57 | 78 II | 1 42 20 | 32 0 | 3 | 81 | 84 III | 11 3 54 | 29 27 | 8 | 178 | 186 IV | 13 37 10 | 56 21 | 21 | 52 | 73 V | 14 57 10 | 23 47 | 3 | 49 | 52 VI | 17 11 22 | 43 50 | 5 | 43 | 48 VII | 23 14 16 | 7 27 | 15 | 52 | 67 +--------------------+---------+-------+-----+------- Total| | | 76 | 512 | 588 -------+--------------------+---------+-------+-----+------- If very faint stellar images could be used for reference, this error could be largely reduced. It was necessary, however, to use stars from the catalogues of the Astronomische Gesellschaft for reference, and with the long exposures required for the faint nebulae the images of these stars were very large. At the edge of the plate, for instance, the arrow-shaped image of a star of the ninth magnitude would often be fully a minute of arc in length. It seemed inadvisable to make an exhaustive study of this magnitude-error, whence the alternatives were to use a restricted portion of the field or to sacrifice accuracy in the reduced positions. The second of these evils was chosen. The positions of the optical centers of images at various distances from the center of the field were determined empirically. Pairs of plates of a region were taken with apertures of 9 inches and with the full 24 inches and were compared in the Zeiss “blink” comparator. With the smaller aperture, and hence the smaller focal ratio, the images near the edge of the plates were sensibly round and small. Superimposed on the 24-inch images, they indicated where the wires should be set in measuring the larger distorted images. Trials were then made, measuring positions of A.G. stars all over the 24-inch plates, until a kind of technique was acquired. Judged by the aims in view and the results obtained, this empirical scheme fully justified itself. At least two plates of each field were taken. In any case the two best plates were put on the “blink” comparator, and only those objects clearly nebulous on both plates were marked. The better plate was then placed on a Gaertner measuring machine. The nebulae and all the A.G. stars fainter than the seventh magnitude were measured in _X_ and _Y_ with the same screw. After an interval of a day or two the plate was remeasured. Settings were read to 0.01 mm, corresponding to about 0.87" on the scale of the plate. The two measures of a nebula differed but seldom in this unit, and if faint reference stars could have been used, a higher degree of accuracy could have been maintained throughout the work. In order to orient the plate, two stars were selected with as large a difference in right ascension and as small a difference in declination as possible. The difference in _X_ was then computed in millimeters, assuming a scale-value of 87.4″ per mm. The plate was placed in the measuring machine with the meridian roughly perpendicular to the screw, and adjusted with the tangent slow-motion until the setting on the two stars gave the computed difference to the limit of accuracy of the settings. This method reduced the constant of orientation of the plate to an almost negligible quantity. Turner’s method (_The Observatory_, 16, 373, 1893) was used as the basis for reducing the measures. The six plate-constants for each field were determined from the five or six A.G. stars most symmetrically distributed about the optical center, and graphs were constructed from which the values of _Y_-_Y₀_ and _X_-_X₀_ were corrected. The Δα and Δδ were then added directly to the α₀ and δ₀ of the assumed center, and final corrections to the positions were read from graphs constructed from Turner’s formulae. Any A.G. stars not included in the determination of plate-constants furnished checks. Since the distribution of the stars was about the same as that of the nebulae, it was hoped that the reduced positions of the latter would be of the same order of accuracy as those of the stars. For the 62 A.G. stars on the seven plates measured, the average difference from the A.G. positions was 1.0″ in either co-ordinate. The settings on the nebulae could be made with greater precision than on the stars, hence these results justify placing the accuracy of the nebular positions at about 2.0″ in either co-ordinate, except for such as were near the edge of the plates. The positions are given for the epoch of the A.G. catalogues, 1875.0. Two of the N.G.C. nebulae had been measured by Lorenz from photographs made at Heidelberg. A comparison of his measures with the present measures shows the same second of arc in declination and the same tenth of a second of time in right ascension. The agreement is perfect to the last units used in the present paper, but as the nebulae, N.G.C. 7619 and 7626, are situated near the center of the plate, they cannot serve as a test of the accuracy of those near the edge. In several cases comparisons could be made with positions from visual measures, as given in the _Strassburg Annals_, Vols. III and IV. Here the agreement is not so good. In one case, on the same night, positions of four objects were measured with reference to a certain star, which was, in turn, tied up to an A.G. star some distance away. The objects are given as N.G.C. 3550, 3552, 3554, and a nova which is designated as K₁₂. The photograph shows N.G.C. 3550 and 3554 properly placed with reference to the star, both in distance and in position-angle; there is nothing at all in the place given for N.G.C. 3552; K₁₂ is properly placed from the star, but is in the N.G.C. position for No. 3552. The position of the reference star is given as about 17″ too small in declination. K₁₂ is clearly N.G.C. 3552, and evidently the fourth object does not exist in the published position. As these objects were all in the same field of view in the telescope, one is at a loss to account for the discrepancy. A list of the comparisons is given in Table II. The descriptions indicate form, brightness, and size, and occasionally the location of a neighboring star. Wolf’s classification was used. It is, as he remarks, wholly empirical and probably without physical significance, yet it offers the best available system of filing away data, and will later be of great service when a significant order is established. One class was interpolated between g and h, and was designated g₀. Brightness was estimated in the order B, pB, pF, F, vF, eF, eeF, and eeeF. The range is from Herschel’s Class II down to the limit of the plates. For several of the fields diameters were estimated to the nearest 5″. Otherwise the size was given in the order L, pL, pS, cS, S, vS, eS. The classification given in Table III is illustrated in Plate III, copied from Wolf’s engraving in Band III, No. 5, of the _Publicationen des Astrophysikalischen Instituts Königstuhl-Heidelberg_. The most striking feature is the great predominance of the classes e and f. These two classes form a continuous sequence from the brightest in the list to the very limits of the plates, where they are but mere faint markings on the films. Eleven are clearly spirals, and the spindles are unexpectedly common. These results are typical. The frequency of the classes e and f may merely be a way of stating that the scale of the telescope is too small to show the ordinary structure, but it must be remembered that many members of these classes are pretty large and bright and that the gradation in the series is apparently continuous. As far as telescopes of moderate focal length are concerned, the predominant form of nebulae as we know them at present is not the spiral, but is this same “e, f” class, described as round or nearly so, brightening more or less gradually toward the center, and devoid of detail. The brightest of the class are probably Messier 60 and N.G.C. 3379. Their spectrum, as derived from objective-prism plates, is continuous, and is probably of the same type as those of the spirals and the globular clusters. A detailed study on an adequate scale of the brighter members of the class will throw considerable light on the problem of the small nebulae. TABLE II ----------------------------------------- HUBBLE _minus_ STRASSBURG --------+----------------+--------------- N.G.C. | Δα | Δδ --------+----------------+--------------- 379 | 0ˢ.0 | + 3″ 380 | +0.1 | + 3 382 | +0.2 | + 1 383 | +0.1 | 0 384 | +0.1 | + 1 385 | +0.1 | + 2 386 | -0.2 | - 2 387 | +0.2 | + 3 3550[2] | +0.5 | +24 3552 | +0.1 | +19 3554 | -0.2 | +15 3558 | -0.3 | - 1 6329 | -0.3 | + 3 6332 | -0.3 | + 6 6336 | +0.1 | + 8 7586 | +0.2 | + 1 7608 | -0.3 | + 6 7611 | -0.2 | - 1 7612[3] | 0.0 | + 2 7617 | +0.1 | + 1 7619[4] | +0.1 | - 1 7623[5] | 0.0 | + 1 7626[6] | -0.2 | - 2 --------+----------------+--------------- [2] Nucleus is eccentric and undefined on the photograph, hence the photographic position is probably in error by several seconds of arc. [3] Mean of the positions given in Vols. III and IV. N.G.C. 7621 is 5ˢ.4 preceding, and 1′ 49″ south of 7623. There is a double star in the position published in the _Strassburg Annals_. [4] Mean of the positions given in Vols. III and IV. N.G.C. 7621 is 5ˢ.4 preceding, and 1′ 49″ south of 7623. There is a double star in the position published in the _Strassburg Annals_. [5] Mean of the positions given in Vols. III and IV. N.G.C. 7621 is 5ˢ.4 preceding, and 1′ 49″ south of 7623. There is a double star in the position published in the _Strassburg Annals_. [6] Mean of the positions given in Vols. III and IV. N.G.C. 7621 is 5ˢ.4 preceding, and 1′ 49″ south of 7623. There is a double star in the position published in the _Strassburg Annals_. TABLE III DISTRIBUTION OF VARIETIES OR CLASSES OF NEBULAE IN THE SEVEN CLUSTERS OR FIELDS ======+=========================================== | FIELD CLASS +----+----+-----+----+----+----+-----+------ | I | II | III | IV | V | VI | VII | Total ------+----+----+-----+----+----+----+-----+------ a | | | 1 | | | | | 1 c | | 1 | | | 1 | | 1 | 3 d | | 1 | 33 | 1 | | | 6 | 41 e | 27 | 39 | 109 | 41 | 27 | 21 | 20 | 284 f | 33 | 35 | 17 | 19 | 8 | 12 | 21 | 145 g | 7 | 3 | 4 | | 12 | 5 | 7 | 38 g₀ | 5 | | 8 | | | 3 | 1 | 17 h | 2 | 2 | 2 | 10 | 1 | 1 | 4 | 22 h₀ | 3 | 2 | 4 | | 1 | 2 | 2 | 14 i | | | | | | 1 | 2 | 3 k | 1 | | 2 | | | | | 3 n | | | | | | | 1 | 1 q | | 1 | | | | | 2 | 3 r | | | | | | 2 | | 2 v | | | | | | 1 | | 1 w | | 1 | 4 | | 2 | | | 7 irreg | | | 1 | 2 | | | | 3 ------+----+----+-----+----+----+----+-----+------ Messier 60 has a spiral as a very near neighbor--H III 44. The contrast in the two classes is well shown; so also in the case of N.G.C. 3379 mentioned above. Here there is a group of three fairly bright nebulae: N.G.C. 3379, a globular nebula of class e; 3389, an open spiral; and 3384, which might be called a spindle, except that the wings flare out from the nucleus. The three irregular forms are N.G.C. nebulae and are commented upon in the descriptions accompanying the positions. Very little can be said concerning the surface-brightness of these objects. It is independent of the distance so long as the angular diameter is sensibly greater than that of a faint star. The photographic plate therefore records the absolute surface-brightness of the nebulae. High luminosity is a comparatively rare attribute and there is some relation between luminosity and absolute size; that is to say, the brighter usually have the greater angular diameter. Since it is hard to conceive of a relation between distance and absolute brightness, the fact that the faint nebulae are usually the smaller can be interpreted only in the light of a relation between luminosity and absolute size. The clustering of the nebulae here recorded is very pronounced. In the center of Field III there are some 75 nebulae scattered over an area equal to that subtended by the full moon.[7] In order to examine the distribution of the different sizes, diameters were plotted against frequencies. The small scale of the plates renders the number of smallest diameters very uncertain. Nebulae less than 10″ in diameter might easily be mistaken for stars and overlooked, especially if they are at some distance from the center of the field. The curves resemble probability-curves, as one would expect for random distribution in a cluster at a definite distance. [7] See Plate IV, enlarged from negative R 3352, taken with 120ᵐ exposure on February 26, 1916. The numbers were marked on only those nebulae which promised to be readily visible on the engraving, and which were separated enough to give room for inscribing the number. The B.D. stars are designated by letters, for which the key is as follows. FIELD III STAR B.D. A = +30°2107 B = +30°2108 C = +30°2109 D = +30°2110 E = +30°2115 F = +30°2121 G = +30°2123 H = +29°2123 J = +29°2125 K = +29°2126 L = +29°2128 M = +29°2129 N = +29°2130 P = +29°2133 R = +29°1970 S = +28°1971 TABLE IV DISTRIBUTION ACCORDING TO SIZE OF THE NEBULAE IN THREE FIELDS =========+===================+============== | FIELD | DIAMETER +-------------------+ WOLF’S FIELD | I | III | VII | IN PERSEUS ---------+-----+------+------+-------------- 5″ | | | | 3 10 | 7 | 38 | 5 | 34 15 | 27 | 67 | 12 | 52 20 | 25 | 42 | 18 | 26 25 | 6 | 19 | 10 | 6 30 | 5 | 9 | 4 | 2 35 | 3 | 2 | 4 | 1 40 | 4 | 5 | 4 | 2 45 | 1 | 3 | 3 | 50 | 1 | | 3 | 60 | | | 3 | 90 | | | 1 | ---------+-----+------+------+-------------- Exposures of two hours gave all of the nebulae recorded. Five-hour exposures brightened the images somewhat, but revealed no new ones. The conclusion would seem to be that the limits of the clusters had been reached. This, however, is uncertain, for the longer exposures gave relatively few stars which were not on the plates of shorter exposures. As a matter of fact, the 24-inch reflector at this altitude seems to have a maximum working efficiency at slightly over two hours. Save for very exceptionally clear and steady skies, the longer exposures add much labor for negligibly greater results. The diameters of the faintest stars near the center of the field, with the full aperture, fine sky, and an hour’s exposure, which are of about magnitude 17.5, are about 2.0″. Longer exposures are apparently subject to change of focus, differential refraction, and other disturbances which tend to increase the size of the images unduly, and hence to spread the total light over a larger area. The result is that the value of _p_ in the reciprocity equation _Itᵖ_ = _iTᵖ_ does not remain constant throughout the exposure, but varies, beyond a certain value of _T_, depending on the adjustments of the telescope, the position of the field, and the condition of the sky. However, the effect should be more noticeable on the stars than on nebulae which present surfaces. [Illustration: FIG. 1.--Distribution of size in Wolf’s Nebel Listen Nos. 3 to 14] I have plotted Wolf’s lists of nebulae, Nos. 3-14, in the same manner, converting estimates of size into seconds of arc according to his table. These lists were made from plates taken with the 16-inch (41 cm) Bruce camera, of focal length 203 cm, of the Heidelberg Observatory. The curves (Fig. 1) take the same form, save that for most the maximum frequency is for diameters between 20″ and 25″. One of his lists was made from plates taken with the 30-inch reflector at Königstuhl. It is of a field in Perseus, α = 3ᵸ12ᵐ, δ = +41° 6′. Diameters of the 124 Wolf nebulae and five others were measured from plates taken with the Yerkes 24-inch reflector. This plot (Fig. 2) gives a maximum for diameters around 15″, and the longer focus of Wolf’s 30-inch apparently does not add to the number of small nebulae distinguishable on the plates made with the shorter telescope. TABLE V WOLF’S NEBEL LISTEN NOS. 3-14 =====+================================================= | Diameter List +-----+-----+------+------+------+-------+-------- | 4″ | 6″ | 15″ | 25″ | 60″ | 200″ | >200″ -----+-----+-----+------+------+------+-------+-------- 3 | 205 | 322 | 291 | 280 | 195 | 36 | 6 4 | | 1 | 69 | 153 | 19 | 6 | 1 5 | | 6 | 99 | 106 | 23 | 1 | 3 6 | | 14 | 114 | 72 | 2 | 2 | 1 7 | | 9 | 103 | 156 | 35 | 4 | 12 8 | | 80 | 372 | 243 | 34 | 3 | 9 | | 48 | 174 | 160 | 19 | | 10 | | 3 | 31 | 26 | 2 | | 11 | | | 13 | 60 | 19 | 1 | 12 | | 14 | 61 | 162 | 27 | 10 | 13 | | | 20 | 61 | 26 | 3 | 14 | | 3 | 160 | 296 | 43 | 1 | 1 -----+-----+-----+------+------+------+-------+-------- The evidence, while far from conclusive, appears to indicate the existence of actual clusters of these small nebulae in the sky. If this is true, it is natural to suppose them physically connected, as is the case in star-clusters. It is not possible to form a conception of this state of affairs until some idea of their distance is acquired. Suppose them to be extra-sidereal and perhaps we see clusters of galaxies; suppose them within our system, their nature becomes a mystery. [Illustration: FIG. 2.--Distribution of size of nebulae in Wolf’s Perseus and three Yerkes fields] The question of nebular distances is of first importance, for it is in terms of this quantity that the various dimensions may be expressed. The dark nebulosities, by their very nature, and the great diffuse clouds, some obviously connected with even naked-eye stars, may safely be considered as galactic, and this view is in accord with their low radial velocities with reference to our system. The planetaries have repeatedly been measured for proper motion, with negligible results. Taking a value of 40 km/sec. for the average radial velocity, and an assumed lower limit of 0.02″ for the average annual proper motion, a tentative lower limit for the average distance of the largest, and hence probably the nearest, is found to be about 2000 light-years. There is thus no reason on this ground for placing them outside our system, especially in view of their decidedly systematic galactic distribution. Rotation of these nebulae, as detected by the spectroscope, furnishes a means of relating mass and average density with distance. Assume an axis perpendicular to the line of sight, the mass as concentrated in the nucleus and the individual distant particles as rotating in equilibrium; let α be the radius, _P_ the period of rotation, _M_ the mass, and suppose the rotation to be circular. Then α³/_P²M_ = _C_, a constant. Let the unit of distance be the light-year (LY); of time, the year; of mass, that of the sun (S), then _C_, as computed from the earth-sun system, is about 4 × 10⁻¹⁵. Let α = the angular radius in seconds of arc _d_ = the distance in light-years ρ = the density in terms of earth’s atmosphere at sea-level _v_ = the linear velocity of rotation in km/sec. Then the following relations hold: (1) _M_ = 3.4 × 10⁻⁴ _d_α_v_² (2) ρ = 1.4 × 10⁻⁶ (_v_/_d_α)² (3) _P_ = 9.15 _d_α/_v_ The velocity of escape for the nebula is proportional to α/ρ and hence to _v_. This follows from the assumption that the particles are rotating in equilibrium, and therefore the factor of proportionality is the ratio between parabolic and circular velocity, that is, 1.4, and is independent of the distance. The value of _v_ for those nebulae so far observed is small, ranging from 5 to 10 km. Hence, if the assumptions held only approximately, the velocity of escape would be small and of the same order as that for the earth. Since these nebulae are composed of the lightest gases, it follows that at any save very low temperatures the molecules would escape at a very rapid rate. Certainly the nebulae would dissipate if the temperatures were of the order of that of our own atmosphere. TABLE VI =======+==========+=========+=================+================== _d_ | Diameter | Mass | Period | Density -------+----------+---------+-----------------+------------------ 10 LY | 0.001 LY | 1.2S | 1.5×10² year | 1.8×10⁻⁷ρ 10² | 0.01 | 12. | 1.5×10³ | 1.8×10⁻⁹ 10³ | 0.1 | 120. | 1.5×10⁴ | 1.8×10⁻¹¹ 10⁴ | 1.0 | 1200. | 1.5×10⁵ | 1.8×10⁻¹³ -------+----------+---------+-----------------+------------------ For an assumed typical planetary nebula, 20″ in diameter, rotating with a velocity of 6 km at 10″ from the perpendicular axis, Table VI has been constructed from formulae (1)-(3), expressing the order of magnitude of dimensions in terms of distance. The velocity of escape would be about 8.4 km per second, whatever the distance. Spectroscopic rotation of spirals furnishes an analogous set of formulae, and here the inclination of the axis may be roughly determined from the ratio of the two diameters of the nebulae. Let β be the semi-minor axis, then the formulae will be: (4) _M_ = 3.4 × 10⁻⁴ _d_α_v_² α ( _v_ )² (5) ρ = 1.4 × --- × 10¹²(------) in suns per cu. LY, or β ( _d_α ) α ( _v_ )² = 2.8 × --- × 10⁻⁶(------) in atmospheres β ( _d_α ) α (6) _P_ = 9.15 _d_ --- _v_ The spirals form a continuous series from the great nebula of Andromeda to the limit of resolution, the smaller ones being much the more numerous. Considering them to be scattered at random as regards distance and size, some conception may be formed of their dimensions from the data at hand. The average radial velocity of those so far observed is about 400 km, while the proper motion is negligible. Putting the annual proper motion at 0.05″, the lower limit of the average distance is found to be about 7500 light-years. If they are within our sidereal system, then, as they are most numerous in the direction of its minor axis, the dimensions of our system must be much greater than is commonly supposed. The observations point to very large values for the rotational components of velocity, although the necessarily small scale of the instruments employed in their study renders the measuring difficult. Pease has determined the velocity of rotation for N.G.C. 4594 with some degree of accuracy. At 120″ from the nucleus it amounts to 300 km and varies linearly with the distance outward. V. M. Slipher reports that for the Andromeda nebula the angular rotation is fastest near the nucleus, and that this type of rotation promises to be the more common. Assume a typical spiral 400″ in diameter, with the ratio of the axes of figure as β/α = 0.1, and with rotation perpendicular to the line of sight at a velocity of, say, 200 km at the periphery. These figures are apparently not very different from the average of the two dozen brighter spirals. Table VII gives the dimensions in terms of distance. The velocity of escape is 280 km/sec. At the lower limit of average distance of spirals the typical nebulae would be fifteen light-years in diameter, forty-five million times as massive as our sun, and 3 × 10¹³ as dense as our atmosphere. On the other hand, if the typical spiral nebula is placed at a suitable distance, its dimensions assume the same order of magnitude as those of our own stellar system. The conception of our galaxy set forth by Eddington in his book _Stellar Movements and the Structure of the Universe_ is that the Milky Way forms a ring around a central, slightly flattened cluster. This ring is supposed to rotate in equilibrium so that the stars may remain concentrated in the configurations they now form. Assuming the ratio of the two radii as one to five, and using Eddington’s figures of 2000 parsecs for the distance of the Milky Way, and 10⁹ suns as the mass of the inner cluster, the period and density may be computed and compared with those of the typical nebula placed at a distance such as will make the diameter the same as that of our system. The results are given in Table VIII. TABLE VII ======+========+============+==========+========================== d | α | Mass | Period | Density ------+--------+------------+----------+-------------------------- 10² | 10⁻¹ | 2.7 × 10⁵ | 9 × 10² | 1.4 × 10⁹ suns per cu. LY 10³ | 10⁰ | 2.7 × 10⁶ | 9 × 10³ | 1.4 × 10⁷ 10⁴ | 10¹ | 2.7 × 10⁷ | 9 × 10⁴ | 1.4 × 10⁵ 10⁵ | 10² | 2.7 × 10⁸ | 9 × 10⁵ | 1.4 × 10³ 10⁶ | 10³ | 2.7 × 10⁹ | 9 × 10⁶ | 1.4 × 10¹ ------+--------+------------+----------+-------------------------- TABLE VIII =======+==========+=========+============+==============+=========== | Distance | Radius | Mass | Period | Density -------+----------+---------+------------+--------------+----------- Nebula |6 × 10⁶ LY|6 × 10³LY|1.6 × 10¹⁰ S|5.4 × 10⁷ year| 5.6 × 10⁻¹ Galaxy | |6 × 10³ | 10⁹ | 2.5 × 10⁸ | 1.2 × 10⁻² -------+----------+---------+------------+---------------+---------- The velocities of escape would be about 280 km for the nebula and 170 km for the galaxy. Considering the problematic nature of the data, the agreement is such as to lend some color to the hypothesis that the spirals are stellar systems at distances to be measured often in millions of light-years. The computations by O. H. Truman[8] and by R. K. Young and W. E. Harper[9] of the motion of our system with respect to the spirals, based on the radial velocities of the spirals, are another and stronger argument for the hypothesis. [8] _Popular Astronomy_, =24=, 111, 1916. [9] _Journal of the R.A.S., Canada_, =10=, 134, 1916. The principal objection lies in their apparently systematic distribution with respect to the Milky Way. The matter is usually stated in the form that “spirals avoid the Milky Way.” There are less than 300 nebulae _known_ to be spiral in form. The greatest of them all is just on the border. It is suggested that the spirals seem to follow the distribution of the small faint nebulae. If this is true, the most that can be definitely stated is that they tend to cluster in certain regions of the sky, in one of which the north pole of the galaxy is located. As the small nebulae and the spirals inhabit the same regions of the sky, it is probable that the order of distance of the two classes is the same. Classes e, f, may even turn out to be spirals themselves. This, however, is a question for large instruments, and is outside the scope of the present paper. TABLE IX FIELD I OF NEBULAE ---+-------------------------------+-----+-------------------------- | (1875.0) | | No.|------------------+------------|CLASS| DESCRIPTION | α | δ | | ---+------------------+------------+-----+-------------------------- 1 | 0ᴴ 56ᵐ 35.1ˢ | +31°36′39″ | f | pF, R, 20″d, *14m 20″p. 2 | 39.3 | 31 38 24 | e | F, R, 20″d, *12m 20″n. 3 | 49.0 | 31 22 14 | h₀ | F, mE110°, 60″l. 4 | 0 57 5.7 | 32 4 12 | e | eF, st. *13m 30″np. 5 | 54.5 | 32 17 41 | e | vF, R, 25″d, *14m 30″sf. 6 | 0 58 8.9 | 32 8 33 | e | vF, R, 25″d, *9 1′nf. 7 | 22.3 | 31 33 12 | e | eF st. 8 | 41.8 | 31 45 33 | f | pF, R, S, Δ2 faint*, bM. 9 | 42.7 | 31 17 58 | f | pF, st. 2*13, 14 1.5′p. 10 | 54.7 | 31 16 30 | g | F, cE0°, 30″l. 11 | 58.0 | 31 43 5 | g | F, cE130°, 30″l, bM. 12 | 59.7 | 32 5 33 | e | vF, R, 30″d. 13 | 0 59 13.9 | 31 56 21 | f | vF, st. *16m40″sf. 14 | 28.2 | 31 31 43 | f | vF, st. *15m 1.5′f. 15 | 51.6 | 32 33 48 | g | vF, E140°, 45″l. 16 | 58.2 | 32 1 58 | f | vF, E60°, 20″l 3f*. 17 | 58.8 | 31 41 27 | f | eF, eS. 18 | 1 0 0.7 | 31 54 35 | e | F, st. 19 | 3.6 | 31 18 39 | e | vF, st. d. nuc. 20 | 6.4 | 31 29 19 | e | vF, 1E, 20″l. 21 | 8.2 | 31 42 16 | e | vF, st. 22 | 10.9 | 31 43 12 | h | vF, E90°, 1′l. 23 | 15.0 | 32 24 1 | e | eF, eS 2*10, 11m1′nf. 24 | 18.9 | 31 30 22 | g | vF, cE, S, *15m40″s. 25 | 22.0 | 31 1 42 | e | vF, st. 26 | 22.1 | 32 22 51 | e | eF, R, 30″d, *12m1.5′nf. 27 | 22.9 | 31 31 29 | f | FcE60°1′l, *16m40″np. 28 | 25.0 | 31 45 17 | f | eF, E, eS. 29 | 29.0 | 31 54 48 | h₀ | Fv, mE160°, 40″l*13m1′s. 30 | 33.3 | 31 54 41 | e | eF, E, eS. 31 | 39.3 | 31 25 23 | h | F, mE130°, 1′l. 32 | 43.2 | 32 17 18 | e | vF, R, 40″d, *14m30″s. 33 | 59.1 | 31 35 14 | g | eF, eS, st. 34 | 1 1 3.5 | 32 38 9 | e | vF, cE40°*11m1′nf. 35 | 11.3 | 31 13 16 | h₀ | vF, 310°, 1′l. 36 | 19.6 | 31 47 9 | f | F, S, E60°, *14m1′s. 37 | 24.5 | 31 25 17 | f | F, st. *14m1′np. 38 | 27.8 | 31 52 56 | f | eF, vS, *15m20″p. 39 | 32.7 | 31 45 48 | e | eF, st. in line with 2f*. 40 | 50.3 | 31 45 57 | e | eF, iR, *14m1′s. 41 | 58.8 | 31 25 54 | e | pF, R, 25″d. no nuc. 42 | 1 2 5.5 | 31 34 21 | e | vF, st. *10m20″s. 43 | 20.4 | 31 29 4 | e | vF, R, 45″d. no nuc. 44 | 22.3 | 31 18 42 | f | F, st. and sev f*. 45 | 26.4 | 32 3 22 | e | vF, st. *11m20″s. 46 | 32.0 | 32 6 19 | e | eF, iR*14m30″sf. 47 | 39.7 | 31 30 21 | g | vF, cE80°, S. 48 | 48.5 | 31 47 5 | f | F, st. *15m1′nf. 49 | 49.0 | 31 41 39 | f | eF, vS, *15m30″f. 50 | 49.8 | 31 57 3 | f | eF, st. *14m1′np. 51 | 1 3 5.3 | 31 42 7 | f | vF, st. 2*14m1′f. 52 | 8.0 | 32 14 51 | e | eF, st. 53 | 26.4 | 31 43 18 | f | vF, st. Δ2vF*. 54 | 37.6 | 31 30 51 | f | eF, st. bet. 2*. 55 | 57.6 | 31 55 41 | f | eF, st. *12m15″p. 56 | 1 4 16.4 | 32 2 9 | f | vF, st. bet. 2*. 57 | 1 5 1.6 | 31 48 22 | e | eF, st. *12m1′s. ---+------------------+------------+-----+-------------------------- NEBULAE PREVIOUSLY KNOWN IN FIELD I ------+---------------+------------+----+--------------------------- N.G.C.| | | | 370 | 0ᴴ 59ᵐ 51.6ˢ | +31°44′55″ | g | vF, S, cE20°* 14m30″s. 374 | 1 0 12.5 | 32 7 35 | g₀ | pB, mE10°bet. 2*13m. 376 | 14.3 | 31 40 43 | f | vF. 379 | 22.5 | 31 51 8 | g₀ | pB, cE 0°, 60″×30″. 380 | 24.5 | 31 48 53 | e | pB, R, 40″d. 382 | 30.9 | 31 44 8 | f | pB, R, 20″d. 383 | 32.0 | 31 44 38 | e | pB, R, 1'd bM. 384 | 32.2 | 31 37 26 | g₀ | pB, cE135°, 30″l. 385 | 34.3 | 31 39 4 | f | pB, R, 40″d. 386 | 38.3 | 31 41 35 | f | pF, st. 388 | 54.2 | 31 38 28 | f | F, st. 392 | 1 1 29.1 | 32 27 59 | f | pF, R, 30″d bM, *11m1′ sp. 394 | 31.6 | 32 28 50 | f | F, st. 397 | 36.4 | 32 26 32 | f | vF, st. 398 | 1 2 0.0 | 31 50 50 | f | F, st. 399 | 5.2 | 31 58 1 | g₀ | F E50° 40″l. 403 | 20.0 | 32 5 9 | k | pB, mE90°, 60″×20″. | | | | 387 | 1 0 40.1 | 31 43 23 | f | vF, eS, st. | | | | I.C. | | | | 1618 | 0 59 3.4 | 31 44 31 | g₀ | pF, cE, 150° 25″l, bM. 1619 | 1 0 28.6 | 32 23 57 | f | pF, st. bet. 2*11, 12m. ------+---------------+------------+----+--------------------------- N.G.C. 379 and 372 are probably the same object, with α of 370, and δ the mean of the two N.G.C. positions. There is no other object in the immediate vicinity. 400 } 401 } Faint stars in these positions; no nebulae near. 402 } 390, Faint star, 16m. in this position. No trace of a nebula. TABLE X FIELD II OF NEBULAE ===+===============================+=====+=========== | (1875.0) | | No.+-------------------+-----------+CLASS|DESCRIPTION | α | δ | | ---+-------------------+-----------+-----+----------- 1 | 1ᴴ 39ᵐ 32.1ˢ |+31°52′58″ | f |F, S. 2 | 41.7 | 32 46 3 | e |eF, pS. 3 | 43.4 | 32 4 25 | d |eeF, S. 4 | 46.7 | 31 29 2 | f |vF, S. 5 | 50.4 | 32 7 35 | e |eF, pS. 6 | 55.6 | 31 24 29 | e |eF, eS. 7 | 59.0 | 32 10 21 | f |vF, vS. 8 | 1 40 27.5 | 31 24 17 | h₀ |eeF, S. 9 | 48.3 | 31 30 29 | e |eeF, vS. 10 | 50.4 | 31 37 46 | e |eeF, vS. 11 | 1 41 5.6 | 31 44 9 | e |eF, S. 12 | 8.9 | 31 55 48 | e |vF, vS. 13 | 9.4 | 31 59 34 | f |vF, pS. 14 | 20.2 | 31 53 23 | e |eF, vS. 15 | 32.6 | 32 20 2 | f |vF, S. 16 | 37.1 | 31 55 40 | e |eF, vS. 17 | 47.6 | 32 16 38 | f |eF, vS. 18 | 51.5 | 31 55 50 | e |eeF, S. 19 | 1 42 0.5 | 31 56 38 | e |eeeF S. 20 | 0.8 | 32 28 25 | f |vF, S. 21 | 15.8 | 32 11 28 | g |eF, 30″l. 22 | 16.4 | 31 52 43 | e |eeF, eS. 23 | 21.1 | 31 55 41 | e |eeF, eS. 24 | 23.5 | 31 57 24 | f |F, S. 25 | 31.5 | 32 0 9 | g |vF, S. 26 | 37.8 | 32 42 19 | e |eeF, S. 27 | 41.4 | 32 34 24 | e |eeF, S. 28 | 43.5 | 31 29 20 | f |eeF, eS. 29 | 44.4 | 32 10 20 | g |pF, 30″l. 30 | 50.4 | 32 19 55 | f |vF, S. 31 | 50.9 | 32 47 16 | e |eF, S. 32 | 51.2 | 31 24 50 | e |eeF, eS. 33 | 58.0 | 32 0 4 | e |eeF, eS. 34 | 1 43 2.7 | 32 52 33 | f |eF, S. 35 | 5.3 | 31 51 52 | e |eeeF, eS. 36 | 7.0 | 31 48 17 | f |pF, S. 37 | 7.5 | 32 32 4 | w |eF,40″d. 38 | 7.7 | 31 56 36 | f |vF, vS. 39 | 8.6 | 31 54 15 | e |eeF, eS. 40 | 9.1 | 31 53 1 | f |eF, eS. 41 | 9.3 | 32 6 11 | e |eeF, vS. 42 | 12.0 | 31 52 35 | f |eeF, eS. 43 | 12.2 | 32 22 58 | f |eF, S. 44 | 13.1 | 31 51 39 | h |eeF, S. 45 | 13.2 | 31 59 34 | e |eeF, vS. 46 | 13.4 | 32 2 32 | e |eeF, eS. 47 | 17.9 | 31 57 14 | f |vF, vS. 48 | 19.6 | 32 25 39 | f |vF, vS. 49 | 20.7 | 31 50 3 | h |eeeF, S. 50 | 22.6 | 32 36 9 | e |eeF, vS. 51 | 22.6 | 31 49 17 | e |eeF, S. 52 | 23.8 | 31 47 57 | e |eeF, eS. 53 | 29.5 | 31 52 29 | f |vF, S. 54 | 30.5 | 32 27 43 | f |pF, pS. 55 | 37.6 | 31 53 20 | e |eF, eS. 56 | 39.0 | 31 56 43 | f |eF, eS. 57 | 39.2 | 32 28 21 | f |vF, S. 58 | 39.3 | 32 13 46 | e |eeF, vS. 59 | 39.9 | 31 53 5 | e |eeF, eS. 60 | 43.4 | 31 53 22 | e |eeF, eS. 61 | 46.8 | 31 52 18 | f |eeF, eS. 62 | 48.9 | 32 16 44 | f |eF, vS. 63 | 56.4 | 32 18 51 | f |eF, vS. 64 | 58.8 | 32 0 10 | e |eeeF, vS. 65 | 1 44 0.7 | 32 27 29 | e |eeF, vS. 66 | 0.8 | 32 9 58 | e |eeF, eS. 67 | 1.9 | 32 0 17 | f |vF, vS. 68 | 4.0 | 32 29 4 | e |eeeF, S. 69 | 8.4 | 32 24 6 | e |eF, vS. 70 | 11.3 | 32 24 47 | f |F, pS. 71 | 14.9 | 32 12 48 | e |eeF, vS. 72 | 20.7 | 32 25 54 | f |vF, S. 73 | 24.6 | 32 4 37 | f |eeF, eS. 74 | 24.6 | 32 9 38 | f |eF, eS. 75 | 34.9 | 32 5 34 | f |eeF, eS. 76 | 43.5 | 32 27 34 | e |eeF, pS. 77 | 47.5 | 31 33 13 | f |eF, eS. 78 | 52.7 | 32 24 24 | e |eF, vS. 79 | 56.0 | 32 14 24 | e |eeeF, vS. 80 | 57.4 | 32 4 2 | e |eeF, S. 81 | 1 46 28.6 | 31 22 2 | f |eeF, eS. ---+-------------------+-----------+-----+----------- NEBULAE PREVIOUSLY KNOWN IN FIELD II =====+================+=============+===+====================== I.C. | | | | 1733 | 1ᴴ 43ᵐ 25.6ˢ |+31° 56′ 40″ | f |vF, eS. 1735 | 35.5 | 31 55 32 | c |vF nuc., iR eeF neb., | | | | 60″d. | | | | | 1 42 20.4 | 31 57 55 | q | 270″×30″. Found | | | | visually by Barnard. | | | | Not catalogued. -----+----------------+-------------+---+---------------------- TABLE XI FIELD III OF NEBULAE ----+---------------------------+-----+-------------------------- | (1875.0) | | No. |----------------+----------|CLASS| DESCRIPTION | α | δ | | ----+----------------+----------+-----+-------------------------- 1 | 10ᴴ 59ᵐ 59.4ˢ |+29°22′40″| e | eeF, 25″d. 2 | 11 0 2.1 | 29 23 37 | e | 35″d. 3 | 14.7 | 29 46 56 | e | eF, 30″d. 4 | 22.0 | 29 15 59 | e | vF, 20″d. 5 | 23.5 | 29 5 59 | f | eF, 30″d. 6 | 25.8 | 29 27 21 | f | vF, 30″d. 7 | 42.5 | 28 39 11 | e | ef, 15″d. 8 | 56.1 | 29 20 10 | d | eeF, 30″d. 9 | 11 1 1.0 | 28 51 3 | e | eF, 20″d. 10 | 5.2 | 29 10 31 | e | eF, 25″d. 11 | 19.5 | 29 22 46 | e | eeF, 15″d. 12 | 22.4 | 28 39 12 | w | eF, 30″d, open spiral. 13 | 23.9 | 29 12 21 | e | vF, 25″d. 14 | 24.8 | 29 19 4 | h₀ | eeF, E165°, 35″×10″ 15 | 27.3 | 29 32 18 | d | eeF, 15″d. 16 | 28.4 | 29 5 32 | e | vF, 30″d. 17 | 28.4 | 29 12 58 | d | eF, 20″d. 18 | 29.2 | 29 31 11 | e | eF, 15″d. 19 | 32.3 | 29 6 30 | h₀ | eeF, 3160°. 20 | 36.6 | 29 17 52 | d | eeF, 20″ d, some structure. 21 | 38.6 | 29 17 13 | f | eF, 20″d. 22 | 53.4 | 29 19 33 | e | eF, E60°, 30″×15″. 23 | 56.6 | 29 54 3 | d | eF, 30″d. 24 | 11 2 2.2 | 29 36 46 | d | eeF, 15″d. 25 | 5.7 | 29 50 3 | w | eeF, 45″d, open spiral. 26 | 17.2 | 28 57 27 | e | eF, 20″d. 27 | 24.0 | 28 45 9 | g | eF, E160°, 40″×20″. 28 | 30.3 | 29 33 6 | e | eeF, 10″d. 29 | 36.0 | 31 14 51 | e | vF, 25″d. 30 | 36.4 | 29 43 59 | e | eeF, 10″d. 31 | 37.9 | 29 24 6 | d | eeF, 20″d. 32 | 38.7 | 29 26 44 | e | eeF, 15″d. 33 | 38.8 | 29 44 12 | e | eeF, 15″d. 34 | 39.8 | 29 20 17 | e | eeF, 15″d. 35 | 40.3 | 29 54 55 | e | eeF, 15″d. 36 | 41.2 | 29 27 20 | w | eeF, nuc. 10″d, ring, 30″d. 37 | 41.4 | 28 55 57 | e | eF, 15″d. 38 | 42.8 | 29 23 45 | d | vF, 15″d. 39 | 44.9 | 29 23 51 | e | eF, 10″d. 40 | 47.3 | 29 18 17 | k | vF, E150°, 45″×15″. 41 | 48.0 | 29 43 23 | g₀ | eeF, E40°, 20″×10″. 42 | 48.3 | 29 21 21 | e | eF, 15″d. 43 | 54.0 | 29 21 19 | g₀ | eF, 30″×10″. 44 | 55.7 | 29 35 33 | e | F, 20″d. 45 | 56.6 | 28 55 41 | e | eF, 35″d. 46 | 58.2 | 29 13 50 | g | eeF, E50°, 30″×10″. 47 | 11 3 4.1 | 29 10 39 | a | eeF, 15″d, structure. 48 | 4.3 | 29 38 56 | g₀ | eeF, E80°, 20″×10″. 49 | 21.6 | 29 1 14 | d | eF, 15″d. 50 | 22.6 | 29 18 15 | d | eeF, 20″d. 51 | 23.4 | 29 17 21 | e | vF, 20″d. 52 | 23.6 | 29 39 35 | e | eF, 20″d. 53 | 24.3 | 29 40 11 | e | eeF, 20″d. 54 | 27.9 | 29 9 3 | f | eF, 15″d. 55 | 28.6 | 30 7 9 | f | eeF, 30″d. 56 | 28.7 | 29 0 47 | d | eeF, 15″d. 57 | 30.1 | 28 49 9 | e | eeF, 20″d. 58 | 31.4 | 29 43 22 | e | F, 15″d. 59 | 31.5 | 29 28 6 | e | eF, 15″d. 60 | 32.5 | 29 14 55 | e | eF, 15″d. 61 | 33.4 | 28 57 49 | e | eF, 15″d. 62 | 35.8 | 29 18 9 | f | vF, 20″d. 63 | 38.5 | 29 23 55 | e | eeF, 10″d. 64 | 39.6 | 29 23 9 | a? | eF, 35″×25″. E35°, | | | | a miniature Dumb-bell. 65 | 39.7 | 29 25 39 | e | eeeF, 10″d. 66 | 40.1 | 29 25 48 | e | eeeF, 10″d. 67 | 40.3 | 29 23 57 | e | eeF, 10″d. 68 | 41.3 | 29 21 55 | g₀ | eF, E110°, 30″*10″. 69 | 41.9 | 29 22 21 | e | eF, 20″d. 70 | 43.7 | 30 7 14 | e | eeF, 20″d. 71 | 44.7 | 29 22 38 | e | eeF, 20″d. 72 | 46.2 | 29 28 7 | f | eF, 20″d. 73 | 46.4 | 29 30 25 | d | eF, 15″d. 74 | 49.8 | 29 22 46 | d | eeF, 20″d. 75 | 51.6 | 29 22 53 | e | eeF, 10″d. 76 | 52.4 | 29 22 34 | e | eeF, 15″d. 77 | 52.9 | 29 43 59 | e | eeF, 20″d. 78 | 53.6 | 28 59 39 | e | F, 35″d. 79 | 54.5 | 29 26 1 | d | eeF, 20″d. 80 | 54.7 | 29 23 5 | e | eeF, 20″d. 81 | 55.1 | 29 21 50 | e | eF, 15″d. 82 | 56.7 | 29 26 22 | e | eeF, 15″d, E50°. 83 | 56.9 | 29 34 40 | e | eF, 15″d. 84 | 57.5 | 29 16 59 | e | eF, double nebula, | | | | nuc. 4″ apart. 85 | 57.6 | 29 8 7 | e | eF, 30″d. 86 | 57.7 | 29 27 19 | h₀ | eeF, E140°, 15″×5″. 87 | 11 4 0.8 | 29 17 51 | e | eeF, 10″d. 88 | 1.0 | 28 56 28 | e | eeF, 20″d. 89 | 1.4 | 29 22 15 | e | eF, 15″d. 90 | 1.4 | 29 39 5 | e | eeF, 15″d. 91 | 1.8 | 28 57 21 | e | vF, 30″d. 92 | 3.4 | 29 27 26 | e | eF, 10″d. 93 | 3.7 | 29 29 10 | e | eeF, 20″d. 94 | 2.7 | 29 20 17 | e | vF, 20″d. 95 | 3.8 | 29 2 9 | e | eeF, iR. 96 | 4.4 | 29 27 33 | e | eF, 10″d. 97 | 5.7 | 29 28 23 | e | eeF, 15″d, faint extensions. 98 | 5.8 | 30 14 51 | e | eF, st. 99 | 6.9 | 29 22 50 | e | eF, 15″d. 100 | 7.6 | 28 56 51 | h₀ | eeF, E25°, 30″×10″. 101 | 9.4 | 29 14 23 | e | eeF, 15″d. 102 | 9.9 | 29 29 29 | d | eeF, 10″d. 103 | 10.0 | 28 53 55 | e? | eeF, faint extensions | | | | 60″×40″? 104 | 10.1 | 30 0 27 | d | eF, 30″d. 105 | 10.6 | 29 8 48 | g₀ | eF, E145°, spiral, 40″×20″. 106 | 12.8 | 29 28 58 | h | eeeF, 20″×10″. 107 | 13.4 | 29 23 15 | e | eeF, 15″d. 108 | 13.5 | 29 21 19 | g₀ | eeF, E125°, 25″×15″. 109 | 13.8 | 29 47 14 | d | eeF, 20″d. 110 | 14.2 | 30 0 57 | k | eF, E40°, 34″×20″. 111 | 14.4 | 29 25 24 | e | eF, 15″d. 112 | 15.6 | 29 29 36 | d | eeeF, 10″d. 113 | 18.6 | 28 55 56 | e | eeF, 15″d. 114 | 20.2 | 28 53 6 | f | eeF, 20″d. 115 | 22.8 | 28 54 6 | e | eeF, 20″d. 116 | 27.9 | 29 23 25 | f | eF, 35″d. 117 | 27.9 | 29 26 40 | e? | eeF, 60″×40″, spiral? 118 | 28.4 | 29 22 31 | e | eF, 45″d. 119 | 28.6 | 29 21 58 | d | eeF, 15″d. 120 | 28.6 | 29 25 18 | e | eeF, 10″d. 121 | 30.2 | 29 37 42 | e | eeF, 15″d. 122 | 32.0 | 29 25 37 | d | eeF, 15″d. 123 | 34.4 | 29 21 33 | e | eF, 20″d. 124 | 34.9 | 29 42 1 | e | eF, 20″d. 125 | 35.5 | 29 12 10 | e | eeF, 10″d. 126 | 36.0 | 29 21 0 | e | eF, E60°, 20″×15″. 127 | 37.0 | 29 27 7 | d | eeeF, 15″d. 128 | 38.5 | 28 56 22 | e | eF, st. 129 | 39.4 | 29 24 33 | f | vF, 25″d. 130 | 40.2 | 29 12 57 | e | eeF, 15″d. 131 | 41.8 | 29 27 40 | g | eeF, E95°, 20″ × 10″. 132 | 46.8 | 29 19 18 | g | eeF, 30″ × 15″. 133 | 47.9 | 29 31 9 | d | eeF, 10″d. 134 | 49.3 | 29 26 1 | f | eF, 15″d. 135 | 49.9 | 29 29 19 | e | eeF, 10″d. 136 | 49.9 | 29 14 45 | e | eeF, 15″d. 137 | 50.5 | 29 25 27 | e | eF, 30″d. 138 | 51.5 | 29 22 55 | e | eF, 10″d. 139 | 52.7 | 29 23 21 | e | eF, 10″d. 140 | 54.1 | 29 29 57 | e | eeF, 15″d. 141 | 11 5 3.0 | 28 56 43 | e | vF, 30″d. 142 | 4.7 | 29 16 36 | e | eF, 15″d. 143 | 6.8 | 29 15 53 | e | eeF, 20″d. 144 | 7.6 | 28 53 4 | d | eeF, 15″d. 145 | 11.6 | 29 38 5 | e | eeF, 20″d. 146 | 12.3 | 29 10 1 | d | eF, 20″d. 147 | 13.5 | 30 9 30 | d | eF, 20″d. 148 | 14.4 | 30 6 28 | e | eF, 20″d. 149 | 14.7 | 29 20 38 | w | eF, 25″d, spiral. 150 | 15.6 | 29 8 19 | d | eeeF, 15″d. 151 | 17.1 | 29 29 16 | e | eF, 20″d. 152 | 19.4 | 29 10 52 | g | vF, E40°, 50″ × 20″. 153 | 34.3 | 29 25 10 | d | eeF, 30″d. 154 | 35.5 | 29 15 0 | e | eeF, 30″d. 155 | 43.6 | 28 57 24 | e | eF, 40″d. 156 | 49.2 | 28 42 34 | f | eF, st. 157 | 51.3 | 28 43 12 | e | eeF, 30″d. 158 | 59.6 | 28 57 38 | e | eeF, 30″d. 159 | 11 6 6.9 | 28 44 55 | d | eeF, 30″d. 160 | 9.7 | 29 29 30 | d | eeeF, 20″d. 161 | 10.6 | 28 40 46 | e | eF, 30″d. 162 | 11.8 | 29 4 8 | f | vF, st. 163 | 12.8 | 30 11 16 | e | eeF, 10″d. 164 | 17.5 | 29 25 47 | e | eF, 15″d. 165 | 23.2 | 28 43 55 | f | eeF, 20″d. 166 | 24.9 | 28 39 40 | e | eeF, 30″d. 167 | 27.8 | 28 41 26 | e | eeF, 30″d. 168 | 29.0 | 28 56 22 | e | eeF, 20″d. 169 | 40.9 | 29 20 27 | d | eeeF, 20″d. 170 | 37.7 | 28 33 23 | d | eeeF, 15″d. 171 | 42.7 | 29 37 59 | e | eeF, 20″d. 172 | 44.2 | 29 5 13 | d | eeeF, 15″d. 173 | 50.6 | 29 18 31 | e | eeF, 20″d. 174 | 11 7 11.1 | 28 32 54 | d | eeF, 20″d. 175 | 14.9 | 30 14 45 | e | eF, 20″d. 176 | 19.2 | 29 18 25 | h | eeeF, 30″×10″. 177 | 27.1 | 29 6 26 | f | eF, 20″d. 178 | 32.9 | 28 51 30 | e | eF, 30″d. ====+================+==========+=====+==================== NEBULAE PREVIOUSLY KNOWN IN FIELD III ========================================================= N.G.C.| | | | 3527 |11ᴴ 0ᵐ 31.4ˢ |+29° 12′ 6″| f | vF, 35″d. 3536 |11 2 5.3 | 29 9 5 | e | F, 40″d. 3539 | 22.9 | 29 20 56 | g₀| F, E5°, 60″×20″. 3550 |11 3 53.5 | 29 26 47 | | pB, eccentric nuc., 35″ × 25″. 3552 |11 3 52.2 | 29 24 38 | e | F, 20″d. 3554 |11 3 57.7 | 29 22 15 | e | vF, 25″d. 3558 |11 4 10.9 | 29 13 17 | f | vF, 15″d, with what appears | | | | to be a faint ring 50″ in d. 3561 | 11 4 28.4 | 29 22 31 | e | eF, 45″d. ------+-------------+-----------+---+------------------------- TABLE XII FIELD IV OF NEBULAE[10] ===+==============================+=====+================= | (1875.0) | | No.|------------------------------|CLASS| DESCRIPTION | α | δ | | ---+------------------+-----------+-----+----------------- 1 |13ᴴ 32ᵐ 33.0ˢ |+56°18′28″ | e | F, eS, *15m10″n. 2 |13 33 0.4 | 56 49 46 | e | eeF, pS. 3 | 16.0 | 55 49 23 | e | eF, S. 4 | 41.7 | 57 9 1 | e | eF, S. 5 | 55.6 | 56 5 4 | e | vF, eS. 6 | 56.9 | 56 6 15 | e | eF, S. 7 |13 34 9.1 | 55 50 46 | e | eeF, eS. 8 | 11.3 | 56 32 8 | f | eF, eS. 9 | 25.9 | 56 29 14 | f | eF, eS. 10 | 56.6 | 56 42 36 | e | eF, vS. 11 | 57.7 | 57 0 46 | f | eF, vS. 12 |13 35 4.9 | 56 45 21 | h | eeF, S. 13 | 49.8 | 56 13 38 | h | vF, S. 14 | 52.0 | 56 52 58 | e | eF, cS. 15 | 53.1 | 56 3 25 | e | eeF, eS. 16 |13 36 20.1 | 55 50 25 | e | eeF, eS. 17 | 29.1 | 56 51 25 | e | eF, S. 18 | 33.1 | 55 49 59 | e | eeF, eS. 19 | 33.2 | 56 43 54 | f | eF, eS. 20 | 38.6 | 55 46 18 | e | eeF, eS. 21 | 39.0 | 56 18 33 | h | F, 30″l. 22 | 41.0 | 56 12 2 | d | eeF, S. 23 | 43.7 | 56 42 11 | e | eeF, S, *15m10″s. 24 | 46.2 | 56 48 12 | e | eF, cL. 25 | 49.7 | 56 41 26 | f | eF, S. 26 | 53.6 | 56 48 57 | e | eeF, eS. 27 | 55.7 | 56 27 19 | h | eeF, S. 28 | 56.1 | 56 40 17 | e | eeF, S. 29 |13 37 7.2 | 56 4 29 | f | vF, S. 30 | 11.6 | 55 46 36 | e | eeF, eS. 31 | 19.0 | 56 24 54 | e | eF, S. 32 | 20.2 | 56 26 51 | f | eeF, vS. 33 | 35.5 | 57 7 6 | e | eF, cS. 34 | 46.0 | 56 5 6 | f | eeF, S. 35 | 54.0 | 56 10 12 | h | eeF, S. 36 | 58.2 | 56 9 31 | h | eeF, S. 37 |13 38 4.3 | 56 7 32 | f | eeF, S. 38 | 9.8 | 56 7 11 | f | eeF, eS. 39 | 15.8 | 56 13 9 | e | eeF, eS. 40 | 17.1 | 56 13 57 | f | eF, vS. 41 | 29.1 | 56 16 49 | e | eF, S. 42 | 35.2 | 56 15 5 | h | eF, vS. 43 | 35.4 | 56 13 55 | h | eeF, eS. 44 | 37.3 | 56 14 41 | f | eF, vS. 45 | 47.3 | 56 41 19 | e | eeF, cS. 46 | 52.8 | 55 35 23 | e | eeF, eS. 47 | 56.4 | 56 12 58 | f | eF, vS. 48 |13 39 6.9 | 56 15 45 | e | eeF, eS. 49 | 7.9 | 56 16 31 | h | eF, vS. 50 | 8.1 | 56 5 45 | f | vF, S. 51 | 9.2 | 56 11 45 | e | eeF, eS. 52 | 9.4 | 55 56 14 | e | eeF, eS. 53 | 13.3 | 56 16 32 | f | eeF, vS. 54 | 17.6 | 56 10 33 | e | eeF, eS. 55 | 19.8 | 56 10 50 | e | eeF, eS. 56 | 23.0 | 56 11 40 | e | eF, eS. 57 | 25.1 | 56 16 43 | e | eeF, eS. 58 | 30.3 | 56 26 49 | f | eF, eS. 59 | 31.6 | 56 20 3 | e | eeF, S. 60 | 45.1 | 56 29 5 | f | eF, vS. 61 | 45.7 | 56 34 46 | e | eeF, S. 62 | 54.2 | 56 15 18 | e | eeF, eS. 63 |13 40 3.2 | 56 37 22 | e | eeF, eS. 64 | 5.9 | 56 30 56 | e | eeF, eS. 65 | 5.9 | 56 30 29 | h | eeF, 30″l. 66 | 27.2 | 56 6 27 | e | eeF, vS. 67 |13 41 27.2 | 56 20 38 | e | eF, 60″d. 68 | 38.8 | 55 47 15 | e | eF, eS. 69 | 47.4 | 55 44 54 | f | eF, vS. 70 |13 42 40.2 | 56 15 54 | e | eeF, S. ---+------------------+-----------+-----+----------------- [10] Field IV covers the position of a group of 18 small nebulae announced by E. E. Barnard in _Astronomische Nachrichten_, 125, 369, 1890. The positions there given were rough estimations from the stars B.D. +56°.1679 and B.D. +56°.1682. On the photographs, the nebulae in this region are so small and so crowded that I have been able to identify only three individuals of the group. Barnard’s Nos. 4, 7, and 18 are very probably my Nos. 41, 43, and 62. NEBULAE PREVIOUSLY KNOWN IN FIELD IV ======+==================+=============+===+=============== N.G.C.| | | | 5278 | 13ᴴ 36ᵐ 59.45ˢ |+56°18′ 3.8″ | | 5279 | 37 3.72 | 56 18 14.5 | | 5294 | 40 39.7 | 55 55 2 | f |eF, S, *15m1′np. ------+------------------+-------------+---+---------------- N.G.C. 5278 and 5279 form a double nebula, somewhat similar to Messier 51. 5278 is the nucleus and 5279 is at the tail of the arm. The spiral apparently has but one branch. TABLE XIII FIELD V OF NEBULAE ==================================================================== | (1875.0) | | No. |---------------------------|CLASS| DESCRIPTION | α | δ | | ----+---------------+-----------+-----+----------------------------- 1 | 14ᴴ 53ᵐ 52.5ˢ |+23°10′16″ | e | eF, S, R. 2 | 54.5 | 23 57 39 | e | vF, R, 20″d, *18m40″nf. 3 | 14 54 56.2 | 23 53 37 | g | eF, S, m3. *16m1′.np. 4 | 58.1 | 23 16 56 | e | vF, pS, iR. 5 | 14 55 6.7 | 23 24 32 | f | eF, S. 6 | 16.2 | 24 5 30 | f | F, S, *17m30″n. 7 | 31.4 | 24 6 9 | w | F, 30″d. Spiral. 8 | 35.9 | 23 58 27 | g | vF, mE, 40″l, bet. 2*. 9 | 37.3 | 24 12 53 | e | eF, eS. 10 | 14 56 13.7 | 23 52 21 | g | F, E, spiral? 11 | 17.7 | 24 2 30 | g | F, E180°. 12 | 26.3 | 24 0 51 | h₀ | vF, S, iR. 13 | 27.0 | 24 9 28 | g | F, vS, E. 14 | 28.6 | 23 23 8 | e | vF, S, R, 15″d, no nuc. 15 | 30.0 | 23 54 53 | e | vF, vS, R. 16 | 32.6 | 24 2 47 | f | eF, vS. 17 | 46.4 | 24 3 54 | e | eF, S, iR. 18 | 47.8 | 24 36 4 | e | vF, S, iR. 19 | 51.2 | 23 40 4 | e | vF, vS. 20 | 56.0 | 23 51 10 | e | eF, vS, R. 21 | 58.7 | 23 49 12 | f | eF, vS, R. 22 | 58.7 | 23 50 14 | e | eF, eS, R. 23 | 59.0 | 23 51 41 | g | eF, S, IE. 24 | 14 57 4.3 | 23 51 51 | e | eF, S. 25 | 4.3 | 23 52 8 | f | eF, E. 26 | 6.1 | 24 5 56 | f | F, bet. 2*14, 15m. 27 | 8.4 | 23 47 22 | g | eF, cS, iR. 28 | 8.9 | 24 16 59 | e | eF, S. 29 | 10.3 | 23 50 31 | e | eF, S. 30 | 11.3 | 23 46 44 | e | eF, S. 31 | 11.8 | 23 49 57 | e | eF, S. 32 | 13.6 | 23 53 2 | h | eF, S. 33 | 18.8 | 23 44 22 | g | eF, S. 34 | 24.1 | 23 42 42 | e | eF, cS, iR. 35 | 24.3 | 24 4 40 | e | eF, S, iR. 36 | 26.8 | 23 45 2 | e | eF, vS, iR. 37 | 35.9 | 24 6 37 | e | eF, S. 38 | 41.7 | 24 35 7 | f | eF, S. 39 | 43.0 | 23 24 38 | e | vF, R, 30″d, no nuc. 40 | 51.7 | 24 0 48 | g | eF, vS, Δ with 2*14 and 16m. 41 | 14 58 0.6 | 23 18 4 | c | vF, 25″d, spiral? 42 | 6.8 | 23 11 21 | g | F, cL, mE180°, 80″×15″. 43 | 18.5 | 23 26 30 | g | eF, S, 20″d. 44 | 19.8 | 23 21 55 | f | vF, R? 60″d. 45 | 25.9 | 23 25 35 | e | eF, S, R, 20″d. 46 | 48.4 | 23 40 57 | g | eF, cS, mE. 47 | 54.7 | 23 54 12 | e | F, mE 180°. 48 | 14 59 56.8 | 24 10 32 | e | vF, S, iR, bM. 49 | 15 0 7.2 | 23 52 11 | e | eF, S, iR. ----+---------------+-----------+-----+----------------------------- NEBULAE PREVIOUSLY KNOWN IN FIELD V ========================================================= N.G.C.| | | | 5829 | 14ᴴ 57ᵐ 9.6ˢ | +23°49′29″ | w | open 2br, spiral. | | | | I.C. | | | | 4526 | 14 57 5.9 | 23 50 31 | e | pB, R, 18″d. 4532 | 59 21.7 | 23 44 43 | e | pB, S, E. ------+--------------+------------+---+------------------ I.C. 4526 is connected with N.G.C. 5829. The two form a double nebula fashioned as a miniature of Messier 51. TABLE XIV FIELD VI OF NEBULAE =====+=========================+=====+============================== | (1875.0) | | No. +--------------+----------+CLASS| DESCRIPTION | α | δ | | -----+--------------+----------+-----+------------------------------ 1 |17ᴴ 8ᵐ 16.7ˢ|+44° 5′35″| f | vF, vS, *13m, 1′f. 2 | 29.9 | 43 26 6 | f | vF, vS, st. 3 | 35.2 | 43 23 8 | g | eF, E 60°, *13m40″sp. 4 | 52.6 | 42 57 44 | f | F, S, st. 5 |17 9 2.6 | 44 18 28 | e | vF, vS, *16m, 40″s. 6 | 14.2 | 44 16 11 | e | eF, S, *16m, 40″f. 7 | 17.5 | 43 50 51 | f | vF, sharp nuc. 30″d. 8 | 33.2 | 43 2 38 | e | F, pS, *17m, 1′n. 9 | 35.1 | 44 2 54 | e | F, vS, *15m, 30″f. 10 | 41.1 | 43 38 39 | g₀ | pF, S, mE, 60°*14m, 30″p. 11 | 53.8 | 43 52 2 | e | vF, vS, *17m, 40″n. 12 |17 10 3.4 | 44 12 35 | f | eF, eS, *16m, 30″n. 13 | 23.3 | 43 49 32 | e | vF, vS, bet. 2 vf*. 14 | 25.5 | 43 43 7 | f | vF, vS. 15 | 29.1 | 43 44 48 | e | vF, vS. 16 | 33.0 | 44 4 43 | g | vF, S. 17 | 37.7 | 44 5 32 | e | eF, vS. 18 | 39.0 | 43 42 38 | g | vF, eS, *16m, 40″sf. 19 | 40.2 | 44 5 20 | h | eF, vS. 20 | 46.7 | 43 51 14 | f | vF, vS, *16m, 40″sf. 21 | 52.8 | 43 33 9 | f | vF, S, *16m, 40″sf. 22 | 55.7 | 44 4 8 | g | F, cE 70°, *14m, 40″n. 23 |17 11 16.3 | 43 10 57 | f | vF, S. 24 | 25.9 | 43 25 48 | f | pF, S, *16m, 40″f. 25 | 33.9 | 43 47 21 | g | vF, vs, cE 160°, *15m, 40″np. 26 | 36.7 | 43 42 51 | h₀ | vF, S, cE 120°, faint nuc. 27 | 43.0 | 43 53 35 | g₀ | pF, S, cE 20°, *14m, 1.5′np. 28 | 45.7 | 43 55 42 | f | F, vS, *15m, 40″nf. 29 | 48.6 | 43 58 50 | e | vF, S *13m, 1.5′n. 30 | 57.1 | 44 8 50 | e | eF, es. 31 | 57.8 | 44 8 6 | e | eF, S. 32 | 57.9 | 43 44 57 | e | vF, vS, *15m, 30″f. 33 |17 12 13.3 | 44 2 16 | e | F, eS, *12m, 1′n. 34 | 26.2 | 44 12 21 | e | F, eS. 35 | 37.2 | 44 12 12 | e | F, eS, Δ with 2*12m. 36 | 38.4 | 43 28 52 | f | pF, vS, *1.5′s. 37 | 40.9 | 43 54 40 | h₀ | eF, cE 150°, no nuc. 38 | 44.9 | 43 45 22 | e | vF, vS, Δ with 2*16m. 39 | 50.6 | 43 39 48 | f | vF, eS, Δ with 2 f*. 40 | 51.0 | 43 48 16 | e | vF, vS, *16m, 40″nf. 41 |17 13 4.9 | 43 36 37 | e | eF, vS, *15m, 20″s. 42 | 27.2 | 43 40 39 | e | vF, vS. 43 | 39.2 | 43 44 19 | e | vF, S. -----+--------------+----------+-----+------------------------------ NEBULAE PREVIOUSLY KNOWN IN FIELD VI ======+=================+==========+=====+========================= N.G.C.| | | | 6323 | 17ᴴ 9ᵐ 30.6ˢ |+43°55′42″| i | pF, mE, ns, 40″l. 6329 | 17 10 27.3 | 43 49 40 | f | pF, pL, slE. 6332 | 17 11 15.2 | 43 48 5 | g₀ | pF, pL, E 45°. 6336 | 17 12 30.0 | 43 55 35 | v | pF, open spiral, 45″d. | | | | I.C. | | | | 4645 | 17 10 53.0 |+43°14′40″| e | vF, pS, Δ with 2 faint*. ------+-----------------+----------+-----+------------------------- N.G.C. 6327 is on the plate but was not measured. TABLE XV FIELD VII OF NEBULAE =====+========================+=====+=============================== | (1875.0) | | No. +--------------+---------+CLASS| DESCRIPTION | α | δ | | -----+--------------+---------+-----+------------------------------- 1 |23ᴴ 10ᵐ 25.7ˢ|+8°13′28″| f | st. 14m. 2 |23 11 19.4 | 7 34 13 | e | F, S, *17m30″s. 3 | 39.3 | 7 45 26 | d | vF, R, no nuc., 16m45″ np. 4 | 47.3 | 7 3 55 | f | eF, S, R, no nuc. 5 |23 12 23.1 | 7 18 20 | c | vF, st. nuc. with ring 45″d. 6 | 42.2 | 6 45 7 | d | eF, S, R, no nuc. 7 | 51.1 | 7 2 10 | q | F, 1bM, mE100°, 100, ×20″. 8 |23 13 17.2 | 7 24 12 | h₀ | vF, S, 1E50°*14m30″p. 9 | 19.4 | 7 34 51 | q | F, sharp nuc., mE70°, 80″×20″. 10 | 29.9 | 7 31 15 | f | F, S, E150°. 11 | 33.6 | 8 6 51 | d | eF, pS, R. 12 | 35.4 | 7 52 39 | g | pF, bM, mE150° 40″l. 13 | 41.6 | 7 32 2 | g | eF, vS. 14 | 41.6 | 7 18 13 | e | vF, vS, Δ2 faint *. 15 | 49.1 | 7 2 16 | e | vF, S, Δ2 faint *. 16 | 52.7 | 7 14 52 | h | F, sharp nuc. vmE20°90″×15″. 17 | 56.6 | 7 19 16 | e | eF, pL, no nuc. 18 |23 14 2.4 | 6 51 8 | f | F, S, R, *14m90″n. 19 | 2.9 | 7 38 55 | f | F, S, R, bM. 20 | 18.4 | 7 42 40 | f | F, S, bM. 21 | 24.4 | 7 45 35 | e | eF, vS, *16m30″s. 22 | 31.3 | 7 27 10 | e | eF, vS, bet. 2*. 23 | 34.9 | 7 31 47 | e | vF, S. 24 | 36.0 | 7 30 3 | f | vF, vS. 25 | 36.2 | 7 42 4 | f | vF, vS. 26 | 37.5 | 7 41 4 | f | vF, vS. 27 | 41.8 | 7 29 40 | h | FN, mE160°, 80″×20″. 28 | 41.8 | 7 13 46 | f | pF, vS, bM, Δ with 2 faint *. 29 | 42.4 | 7 44 32 | e | eF, eS,*14m1′sp. 30 | 46.1 | 7 32 31 | n | pFN, eccentric, mE90°. 31 | 46.2 | 7 29 21 | i | pF, vS, R. 32 | 52.8 | 6 40 49 | f | st. 14m. 33 | 54.9 | 7 32 39 | e | F, S, 1E. 34 | 56.2 | 7 10 7 | i | vF, S, E, *14m30″sf. 35 | 56.9 | 6 47 41 | e | vF, 1E, *15m30″s. 36 | 58.5 | 7 33 24 | e | vF, vS, *17m30″f. 37 |23 15 5.9 | 7 51 23 | e | vF, R, lvM,40″d, *12.1′n. 38 | 11.1 | 7 20 15 | f | vF, S, E, *14m30″sp. 39 | 16.9 | 7 34 23 | e | vF, vS, *15m1′np. 40 | 20.4 | 7 38 15 | d | vF, vS. 41 | 21.8 | 8 18 24 | h | vF, E, *9m, superimposed. 42 | 26.0 | 8 23 37 | d | pF, pL, R, lbM. 43 | 28.7 | 7 29 43 | f | F, S. 44 | 53.0 | 8 15 14 | e | eF, pL, iR, no nuc. 45 | 56.3 | 7 46 32 | e | eF, S, *16m40″p. 46 |23 16 24.2 | 7 40 32 | e | vF, E, *17m40″f. 47 | 38.8 | 8 18 39 | h₀ | eF, no nuc., vmE175°, | | | | 150″×30″. 48 | 42.5 | 7 33 39 | g | vF, S, E. 49 | 43.4 | 7 36 39 | e | eF, pS, no nuc. Trapz. of 4*. 50 | 55.3 | 7 51 8 | e | vF, S, *12m1′s. 51 |23 17 14.2 | 7 37 37 | e | eF, vS, *12m2′nf. 52 | 34.9 | 6 55 40 | d | eF, pS, no nuc. -----+--------------+---------+-----+------------------------------- NEBULAE PREVIOUSLY KNOWN IN FIELD VII ------+---------------+---------+-----+-------------------------- N.G.C.| | | | 7604 | 23ᴴ 11ᵐ 31.7ˢ |+6°44′48″| f | F, R, bM. 7605 | 32.6 | 6 41 46 | f | F, R, bM, *15m70″p. 7586 | 36.1 | 7 54 7 | f | pF, st. 7608 | 23 12 55.5 | 7 40 6 | h | pF, sharp nuc., mE20°, | | | | 100″×25″. 7611 | 23 13 16.6 | 7 22 45 | g₀ | pB, gbM, mE140°, 80″×30″. 7612 | 24.7 | 7 53 38 | g | pB, mbM, cE170°, 80″×40″. 7615 | 35.0 | 7 42 58 | f | F, E130°, * 14m involved. 7617 | 49.2 | 7 28 54 | e | pF, pS, mbM, vlE20°. 7619 | 54.8 | 7 31 19 | f | B, R, 90″d. 7621 | 23 14 5.0 | 7 40 56 | g | pF, pS, mbM, E0°. 7623 | 10.4 | 7 42 45 | f | pB, R, mbM, 60″d. 7626 | 22.8 | 7 31 56 | f | B, R, bM, 90″d, *14m60″p. 7631 | 23 15 7.1 | 7 31 59 | g | pB, mbM, mE80°, 110′×40″. 7634 | 22.3 | 8 12 14 | f | F, R, *10m20″p. 2d I.C.| | | | 5309 | 23 12 51.8 | 7 25 32 | g | pF, mbM, E0°, 50″×30″, | | | | *14m on south edge. ------+---------------+---------+-----+-------------------------- YERKES OBSERVATORY May, 1917 [Illustration: PLATE III WOLF’S CLASSES OF NEBULAE (Copied from the Königstuhl [Heidelberg] Publications)] [Illustration: PLATE IV ENLARGED NEGATIVE OF FIELD III23ᴴ 11ᵐ 31ˢ Center at α=11ᴴ 4ᵐ, δ=+29°30′ For identification of lettered stars see footnote 7 page 5.] *** END OF THE PROJECT GUTENBERG EBOOK PHOTOGRAPHIC INVESTIGATIONS OF FAINT NEBULAE *** Updated editions will replace the previous one—the old editions will be renamed. Creating the works from print editions not protected by U.S. copyright law means that no one owns a United States copyright in these works, so the Foundation (and you!) can copy and distribute it in the United States without permission and without paying copyright royalties. Special rules, set forth in the General Terms of Use part of this license, apply to copying and distributing Project Gutenberg™ electronic works to protect the PROJECT GUTENBERG™ concept and trademark. Project Gutenberg is a registered trademark, and may not be used if you charge for an eBook, except by following the terms of the trademark license, including paying royalties for use of the Project Gutenberg trademark. If you do not charge anything for copies of this eBook, complying with the trademark license is very easy. You may use this eBook for nearly any purpose such as creation of derivative works, reports, performances and research. Project Gutenberg eBooks may be modified and printed and given away—you may do practically ANYTHING in the United States with eBooks not protected by U.S. copyright law. Redistribution is subject to the trademark license, especially commercial redistribution. START: FULL LICENSE THE FULL PROJECT GUTENBERG LICENSE PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK To protect the Project Gutenberg™ mission of promoting the free distribution of electronic works, by using or distributing this work (or any other work associated in any way with the phrase “Project Gutenberg”), you agree to comply with all the terms of the Full Project Gutenberg™ License available with this file or online at www.gutenberg.org/license. Section 1. General Terms of Use and Redistributing Project Gutenberg™ electronic works 1.A. By reading or using any part of this Project Gutenberg™ electronic work, you indicate that you have read, understand, agree to and accept all the terms of this license and intellectual property (trademark/copyright) agreement. If you do not agree to abide by all the terms of this agreement, you must cease using and return or destroy all copies of Project Gutenberg™ electronic works in your possession. If you paid a fee for obtaining a copy of or access to a Project Gutenberg™ electronic work and you do not agree to be bound by the terms of this agreement, you may obtain a refund from the person or entity to whom you paid the fee as set forth in paragraph 1.E.8. 1.B. “Project Gutenberg” is a registered trademark. It may only be used on or associated in any way with an electronic work by people who agree to be bound by the terms of this agreement. There are a few things that you can do with most Project Gutenberg™ electronic works even without complying with the full terms of this agreement. See paragraph 1.C below. There are a lot of things you can do with Project Gutenberg™ electronic works if you follow the terms of this agreement and help preserve free future access to Project Gutenberg™ electronic works. See paragraph 1.E below. 1.C. The Project Gutenberg Literary Archive Foundation (“the Foundation” or PGLAF), owns a compilation copyright in the collection of Project Gutenberg™ electronic works. Nearly all the individual works in the collection are in the public domain in the United States. If an individual work is unprotected by copyright law in the United States and you are located in the United States, we do not claim a right to prevent you from copying, distributing, performing, displaying or creating derivative works based on the work as long as all references to Project Gutenberg are removed. Of course, we hope that you will support the Project Gutenberg™ mission of promoting free access to electronic works by freely sharing Project Gutenberg™ works in compliance with the terms of this agreement for keeping the Project Gutenberg™ name associated with the work. You can easily comply with the terms of this agreement by keeping this work in the same format with its attached full Project Gutenberg™ License when you share it without charge with others. 1.D. The copyright laws of the place where you are located also govern what you can do with this work. Copyright laws in most countries are in a constant state of change. If you are outside the United States, check the laws of your country in addition to the terms of this agreement before downloading, copying, displaying, performing, distributing or creating derivative works based on this work or any other Project Gutenberg™ work. The Foundation makes no representations concerning the copyright status of any work in any country other than the United States. 1.E. Unless you have removed all references to Project Gutenberg: 1.E.1. The following sentence, with active links to, or other immediate access to, the full Project Gutenberg™ License must appear prominently whenever any copy of a Project Gutenberg™ work (any work on which the phrase “Project Gutenberg” appears, or with which the phrase “Project Gutenberg” is associated) is accessed, displayed, performed, viewed, copied or distributed: This eBook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook. 1.E.2. If an individual Project Gutenberg™ electronic work is derived from texts not protected by U.S. copyright law (does not contain a notice indicating that it is posted with permission of the copyright holder), the work can be copied and distributed to anyone in the United States without paying any fees or charges. If you are redistributing or providing access to a work with the phrase “Project Gutenberg” associated with or appearing on the work, you must comply either with the requirements of paragraphs 1.E.1 through 1.E.7 or obtain permission for the use of the work and the Project Gutenberg™ trademark as set forth in paragraphs 1.E.8 or 1.E.9. 1.E.3. If an individual Project Gutenberg™ electronic work is posted with the permission of the copyright holder, your use and distribution must comply with both paragraphs 1.E.1 through 1.E.7 and any additional terms imposed by the copyright holder. Additional terms will be linked to the Project Gutenberg™ License for all works posted with the permission of the copyright holder found at the beginning of this work. 1.E.4. Do not unlink or detach or remove the full Project Gutenberg™ License terms from this work, or any files containing a part of this work or any other work associated with Project Gutenberg™. 1.E.5. Do not copy, display, perform, distribute or redistribute this electronic work, or any part of this electronic work, without prominently displaying the sentence set forth in paragraph 1.E.1 with active links or immediate access to the full terms of the Project Gutenberg™ License. 1.E.6. You may convert to and distribute this work in any binary, compressed, marked up, nonproprietary or proprietary form, including any word processing or hypertext form. However, if you provide access to or distribute copies of a Project Gutenberg™ work in a format other than “Plain Vanilla ASCII” or other format used in the official version posted on the official Project Gutenberg™ website (www.gutenberg.org), you must, at no additional cost, fee or expense to the user, provide a copy, a means of exporting a copy, or a means of obtaining a copy upon request, of the work in its original “Plain Vanilla ASCII” or other form. Any alternate format must include the full Project Gutenberg™ License as specified in paragraph 1.E.1. 1.E.7. Do not charge a fee for access to, viewing, displaying, performing, copying or distributing any Project Gutenberg™ works unless you comply with paragraph 1.E.8 or 1.E.9. 1.E.8. You may charge a reasonable fee for copies of or providing access to or distributing Project Gutenberg™ electronic works provided that: • You pay a royalty fee of 20% of the gross profits you derive from the use of Project Gutenberg™ works calculated using the method you already use to calculate your applicable taxes. The fee is owed to the owner of the Project Gutenberg™ trademark, but he has agreed to donate royalties under this paragraph to the Project Gutenberg Literary Archive Foundation. Royalty payments must be paid within 60 days following each date on which you prepare (or are legally required to prepare) your periodic tax returns. Royalty payments should be clearly marked as such and sent to the Project Gutenberg Literary Archive Foundation at the address specified in Section 4, “Information about donations to the Project Gutenberg Literary Archive Foundation.” • You provide a full refund of any money paid by a user who notifies you in writing (or by e-mail) within 30 days of receipt that s/he does not agree to the terms of the full Project Gutenberg™ License. You must require such a user to return or destroy all copies of the works possessed in a physical medium and discontinue all use of and all access to other copies of Project Gutenberg™ works. • You provide, in accordance with paragraph 1.F.3, a full refund of any money paid for a work or a replacement copy, if a defect in the electronic work is discovered and reported to you within 90 days of receipt of the work. • You comply with all other terms of this agreement for free distribution of Project Gutenberg™ works. 1.E.9. If you wish to charge a fee or distribute a Project Gutenberg™ electronic work or group of works on different terms than are set forth in this agreement, you must obtain permission in writing from the Project Gutenberg Literary Archive Foundation, the manager of the Project Gutenberg™ trademark. Contact the Foundation as set forth in Section 3 below. 1.F. 1.F.1. Project Gutenberg volunteers and employees expend considerable effort to identify, do copyright research on, transcribe and proofread works not protected by U.S. copyright law in creating the Project Gutenberg™ collection. Despite these efforts, Project Gutenberg™ electronic works, and the medium on which they may be stored, may contain “Defects,” such as, but not limited to, incomplete, inaccurate or corrupt data, transcription errors, a copyright or other intellectual property infringement, a defective or damaged disk or other medium, a computer virus, or computer codes that damage or cannot be read by your equipment. 1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the “Right of Replacement or Refund” described in paragraph 1.F.3, the Project Gutenberg Literary Archive Foundation, the owner of the Project Gutenberg™ trademark, and any other party distributing a Project Gutenberg™ electronic work under this agreement, disclaim all liability to you for damages, costs and expenses, including legal fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH DAMAGE. 1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a defect in this electronic work within 90 days of receiving it, you can receive a refund of the money (if any) you paid for it by sending a written explanation to the person you received the work from. If you received the work on a physical medium, you must return the medium with your written explanation. The person or entity that provided you with the defective work may elect to provide a replacement copy in lieu of a refund. If you received the work electronically, the person or entity providing it to you may choose to give you a second opportunity to receive the work electronically in lieu of a refund. If the second copy is also defective, you may demand a refund in writing without further opportunities to fix the problem. 1.F.4. Except for the limited right of replacement or refund set forth in paragraph 1.F.3, this work is provided to you ‘AS-IS’, WITH NO OTHER WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PURPOSE. 1.F.5. Some states do not allow disclaimers of certain implied warranties or the exclusion or limitation of certain types of damages. If any disclaimer or limitation set forth in this agreement violates the law of the state applicable to this agreement, the agreement shall be interpreted to make the maximum disclaimer or limitation permitted by the applicable state law. The invalidity or unenforceability of any provision of this agreement shall not void the remaining provisions. 1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the trademark owner, any agent or employee of the Foundation, anyone providing copies of Project Gutenberg™ electronic works in accordance with this agreement, and any volunteers associated with the production, promotion and distribution of Project Gutenberg™ electronic works, harmless from all liability, costs and expenses, including legal fees, that arise directly or indirectly from any of the following which you do or cause to occur: (a) distribution of this or any Project Gutenberg™ work, (b) alteration, modification, or additions or deletions to any Project Gutenberg™ work, and (c) any Defect you cause. Section 2. Information about the Mission of Project Gutenberg™ Project Gutenberg™ is synonymous with the free distribution of electronic works in formats readable by the widest variety of computers including obsolete, old, middle-aged and new computers. It exists because of the efforts of hundreds of volunteers and donations from people in all walks of life. Volunteers and financial support to provide volunteers with the assistance they need are critical to reaching Project Gutenberg™’s goals and ensuring that the Project Gutenberg™ collection will remain freely available for generations to come. In 2001, the Project Gutenberg Literary Archive Foundation was created to provide a secure and permanent future for Project Gutenberg™ and future generations. To learn more about the Project Gutenberg Literary Archive Foundation and how your efforts and donations can help, see Sections 3 and 4 and the Foundation information page at www.gutenberg.org. Section 3. Information about the Project Gutenberg Literary Archive Foundation The Project Gutenberg Literary Archive Foundation is a non-profit 501(c)(3) educational corporation organized under the laws of the state of Mississippi and granted tax exempt status by the Internal Revenue Service. The Foundation’s EIN or federal tax identification number is 64-6221541. Contributions to the Project Gutenberg Literary Archive Foundation are tax deductible to the full extent permitted by U.S. federal laws and your state’s laws. The Foundation’s business office is located at 809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887. Email contact links and up to date contact information can be found at the Foundation’s website and official page at www.gutenberg.org/contact Section 4. Information about Donations to the Project Gutenberg Literary Archive Foundation Project Gutenberg™ depends upon and cannot survive without widespread public support and donations to carry out its mission of increasing the number of public domain and licensed works that can be freely distributed in machine-readable form accessible by the widest array of equipment including outdated equipment. Many small donations ($1 to $5,000) are particularly important to maintaining tax exempt status with the IRS. The Foundation is committed to complying with the laws regulating charities and charitable donations in all 50 states of the United States. Compliance requirements are not uniform and it takes a considerable effort, much paperwork and many fees to meet and keep up with these requirements. We do not solicit donations in locations where we have not received written confirmation of compliance. To SEND DONATIONS or determine the status of compliance for any particular state visit www.gutenberg.org/donate. While we cannot and do not solicit contributions from states where we have not met the solicitation requirements, we know of no prohibition against accepting unsolicited donations from donors in such states who approach us with offers to donate. International donations are gratefully accepted, but we cannot make any statements concerning tax treatment of donations received from outside the United States. U.S. laws alone swamp our small staff. Please check the Project Gutenberg web pages for current donation methods and addresses. Donations are accepted in a number of other ways including checks, online payments and credit card donations. To donate, please visit: www.gutenberg.org/donate. Section 5. General Information About Project Gutenberg™ electronic works Professor Michael S. Hart was the originator of the Project Gutenberg™ concept of a library of electronic works that could be freely shared with anyone. For forty years, he produced and distributed Project Gutenberg™ eBooks with only a loose network of volunteer support. Project Gutenberg™ eBooks are often created from several printed editions, all of which are confirmed as not protected by copyright in the U.S. unless a copyright notice is included. Thus, we do not necessarily keep eBooks in compliance with any particular paper edition. Most people start at our website which has the main PG search facility: www.gutenberg.org. This website includes information about Project Gutenberg™, including how to make donations to the Project Gutenberg Literary Archive Foundation, how to help produce our new eBooks, and how to subscribe to our email newsletter to hear about new eBooks.