158 



KNOWLEDGE. 



[July 1, 1896. 



PHOTOGRAPH OF THE REGION OF THE 



SPIRAL NEBULA MESSIER 33 TRIANGULI. 



By Is.vAc lloiiEKTs, D.Sc, F.R.S. 



THE photograph was taken with the C'ooko five-inch 

 lens on the 14th November, ls!)5, with exposure 

 of the phito (luring two hours and llftcen minutes. 

 The centre of the plate is about 1!.A. Hi. 2Hm., 

 declination north 80' 7' ; and the area of the slcy 

 covered is 8-1 degrees from north to south and CI degrees 

 from piri-t'diiHi to fiiUitii'nvi, the nebula being at the centre. 



Scale, one millimetre to one hundred and twenty-one 

 seconds of arc. 



Sir .T. llerschel (N. G. C, No. TiOH ; (i. C, No. 352) and 

 Lord Rosse {( 'hue r rat ions of Nihulm mid Clustns of Stars, 

 p. 20) record many observations made by them of this spiral 

 nebula, and by the aid of their large instruments, used with 

 great skill and perseverance, they accomplished all that 

 was possible in the way of descriptive matter and delineation 

 to present the object in an intelligible form to astronomers. 

 It is no adverse reflection upon their work if they did 

 not succeed in the accomphshment of their object, for 

 such is the vast area of the nebula, the complexity of 

 its structure, and the faintness of parts of the nebulosity, 

 that the best efforts by eye and hand could not possibly 

 delineate it. 



The photograph shows the nebula to be about sixty-two 

 minutes of arc in length from north foUowimj to south 

 precedimj, and thirty-five minutes in breadth from south 

 foUomng to north precedimj. 



There are two large, very prominent spiral arms, with 

 their respective curvatures facing north and south, and the 

 curves are approximately symmetrical from their extremi- 

 ties to their point of junction at the centre of revolution, 

 where there is a nebulous star, of about tenth magnitude, 

 with dense nebulosity surrounding it — elongated in north 

 and south directions. Involved in this nebulosity are three 

 bright stars and several faint nebulous stars ; the two arms 

 are also crowded with well-defined stars and faint nebulous 

 stars with nebulosity between them, and it is to the com- 

 bined effect of these that the defined forms of the arms 

 are due. There are also subsidiary arms, less well-defined, 

 trending towards the centre of revolution, which are con- 

 stituted of interrupted streams of faint stars and nebulosity 

 intermingled together. 



There are detached outliers of nebulosity with many 

 small well-defined stars as well as nebulous stars involved 

 in them ; also isolated nebulous stars ou the extreme 

 boundaries of the nebula. 



The larger photograph taken with the twenty-inch 

 reflector simultaneously with that here annexed shows 

 more clearly the details referred to, but the area of the sky 

 delineated is limited to four square degrees. 



In studying these photographs the question is very 

 naturally presented to us, What is the cause that pro- 

 duced this vast stellar and nebulous whirlpool in space ? 

 Two answers may be suggested : — (1) An explosive dis- 

 ruption of a large body ; (2) collision between two bodies 

 moving from opposite directions. The colliding bodies 

 might be two stars, two nebulse, or two meteor streams ; 

 and if we judge by the widely scattered vortical distribution 

 of the star-like and nebulous matter shown on the photo- 

 graphs, it is very probable that the collision of two streams 

 of meteorites would be the cause. 



Many other spiral nebulie have already been photo- 

 graphed, and the appearance of each of them would well 

 fit into the hypothesis suggested by Prof. Lockyer of the 

 collision of streams of meteoric matter. 



Noticts of Boolis. 



Rcmorkahle F.riipsrs, by W. T. Lynn (Edward Stanford, 

 Gd.), is apologetically presented by the author as but " a 

 little one." Here the apology is scarcely appropriate, for 

 many readers would gladly see a larger work, tracing and 

 explaining the allusions to astronomy in ancient and 

 mediiBval literature, from Mr. Ijynn's pen. Mr. Lynn 

 roughly divides the book into two periods — first, that 

 of those eclipses which took place prior to a.i>. 171.'), 

 the year when the prominences wore first seen ; the 

 other, that of those subsequent to that date. The first 

 authentic recorded eclipse he dates as recently as n.c 

 776, as found in the "Str-Kimj," which is Mr. Lynn's 

 free rendering of the title of the Chinese chronicle 

 the " Shu C/iiui/." Rut according to a series of papers 

 on " Some Astronomical Records in Ancient Chinese 

 Books," published in "The Observatory" in 18U5, a 

 noteworthy eclipse took place at An Yi Hsien on October 

 22nd, 213G n.c, from 10 to 12.30 in the daytime, 

 which may therefore surely be allowed a place in eclipse 

 history. Mr. Lynn has long been known as a first 

 authority on ancient eclipses, and the first portion of this 

 his most recent work ably sustains his reputation. The 

 latter part is the most lucid and accurate compendium of the 

 results of modern eclipses that we have seen in such small 

 compass. On page 38, however, he has been led into 

 error on one point. Speaking of the eclipse of 1878 he 

 says, " The corona was smaller and less brilliant than in 

 those of the last-mentioned eclipses" — i.e., 1809, 1870, and 

 1871. This was scarcely the case. As to its form, it was 

 indeed of a most strongly marked minimum type, but it 

 was of unusual extent and more than average brilliancy. 

 These are the only corrections we note in a most readable 

 and convenient little manual, the low price of which 

 should certainly secure it a large sale. 



Historical and Future Eclipsrs. By Rev. S. J. .lohnson, 

 M.A., F.R.A.S. (Parker & Co.) illustrated. 4s. 6d. 

 We are sorry not to be able to accord Mr. Johnson's 

 book by any means unqualified praise. It is in effect a 

 second edition of "Eclipses, Past and Future," published 

 by the same author in 1874, and to which a small 

 supplement was added in 1889. As it originally appeared 

 the book had very considerable merits. It passed in 

 brief but sufficient review nearly all the more important 

 eclipses of the past, and gave some interesting particulars 

 of a large number of eclipses to come. But in a second 

 edition, published after an interval of almost a quarter of 

 a century, we expect to find not merely all the information 

 of the first edition, but also its errors corrected and its 

 general character improved. The reverse is the case. The 

 information given in the original work concerning the 

 eclipses of 1896 to 1900 — those most important to us just 

 now — is not expanded but expunged. The misprint of 

 " Ophinchus " for " Ophiuchus " — excusable, perhaps, in a 

 first edition — is developed systematically throughout the 

 present book. The physical details respecting the sun and 

 planets, meagre enough in the earlier volume, remain 

 nearly in the same condition, no sustained attempt having 

 been made to bring them up to date ; whilst the last page 

 of the book repeats a long-exploded idea. The new matter 

 is not always correct. Oppolzer's " Canon " is stated not 

 to give solar eclipses in the southern hemisphere. Curiously 

 enough, whilst the particulars of the eclipses close at hand 

 are wholly eliminated, and those relatively near are often 

 much shortened, the list of future eclipses is carried up to 

 2491, several centuries further than before. In short, a 

 work with much to recommend it, and which, with a little 



