Oct. 25, 1883] 



NATURE 



621 



are now presented, will no doubt tend to convey a strong 

 impression of great and rapid changes undergone by the 

 nebula itself. I am far from participating in any such 

 impressirn. Comparing only my own drawings made at 

 epochs (1824 and 1837) differing by thirteen years, the 

 disagreements, though confessedly great, are not more 

 than I am disposed to attribute to inexperience in such 

 delineations (which are really difficult) at an early period 

 —to the far greater care, pains, and time bestowed upon 

 the later drawings. . . . Now there is only one particular 

 on which I am at all inclined to insist as evidence of 

 change, viz., in respect of the situation and form of the 

 nebula oblongata, which my figure of 1824 represents as a 

 tolerably regular oval. ...No observer now, I think, 

 looking ever so cursorily at this point of detail, would 

 represent the broken, curved, and unsymmetrical nebula 

 m question ... as it is represented in the earlier of the 

 two figures.'' 



The enormous body of work done even in Sir J. 

 Herschel's time, chiefly by Lassell, Bond, Liaponoff, 

 Struve, and Lord Rosse, is so fully recorded that it is 

 impossible to do more than refer to it in the space at our 

 disposal, besides which much of it is so recent as to be 

 still in the minds of all interested in such questions. But 



,t 2; ~^ , Map of ihe Huygfcenan Regkn.-A, the Huyghcnia 



rJ^M '■ ™ S G E mil L'- ; D ' R ™<»™-- E. Kegio Gentiliana; I 

 Regio Messienana-Brachium Messien, Proboscis Major; G. Regie- 

 J 'erhemiana : H, Sinus Magnus; I, Scbriter's Bridge. 



Mr. Holden, in his work on the nebula, has not contented 

 himself with discussing this work merely. The Washington 

 observations made by himself are given, and cover nearly 

 100 pages. 



We may now deal with the results arrived at. Prof. 

 Holden considers the evidence of change undoubted, but 

 such change depends less upon actual change of form 

 than upon shiftings of the maxima of brightness. The 

 most undoubted changes are in the brightness of the first 

 and second Schrceter's bridge, and in the appearance of the 

 nucleus of the first. The changes in the brightness of 

 some of the masses are established by the Washington 

 observations alone. Among the results of these observa- 

 tions is a new nebulous patch seen from the time of its 

 origin, when it was stellar in appearance, and faint, until 

 now, when it is bright, and of measurable dimensions. 



Another matter investigated by Prof. Holden is the 

 question cf the connection of the stars with the nebula. 

 On this point spectroscopic work is brought upon the 

 scene. The spectrum of the nebula was first studied by 

 Huggins. The gaseous nature of some of the small stars 

 near the trapezium is, Prof. Holden thinks, indicated by 

 their peculiar behaviour under different magnifying 

 powers ; some of them are best seen with low powers. 



The question of photography is introduced in an 

 appendix giving the results obtained by the late Dr 

 Draper just before his lamented death. This photograph 

 was exposed for 137 minutes, and, ac may be easily 

 imagined lacks sharpness, but still, as Prof. Holden puts 

 it, it worthily inaugurated nebular-photography. He also 

 clearly pointed out that, since the eye and the salts of silver 

 do not most strongly respond to light of the same wave- 

 lengths, the intensities of drawings and photographs must 

 vary, and he shows that they do vary. On the other hand, 

 it is shown that the untouched photograph defends the best 

 drawings against the charge of depending too much 

 upon the personal equation of the observer, as over 

 large regions the best drawings are justified by the 

 photograph. 



Mr. Common's photograph, a reprodurtion of which 

 we give, is far finer than Dr. Draper's, among other 

 reasons because it was exposed for about one-third the 

 time, it is to be hoped that we shall have photographs 

 as good as this taken for the future every year, not 

 only on plates responding to blue light, but on plates 

 responding to green and red. In this way most precious 

 records will be secured for future discussion. 



On this question we may make the following quotation- 

 from Mr. Common's communication to the Royal Astro- 

 nomical Society : — 



" To rind if there is any change of form or relative 

 brightness observable in a nebula with any degree of 

 certainty, it will be necessary to compare photographs 

 taken at some undetermined interval of time ; and the 

 best thing to do now seems to me to be to get as many 

 photographs as possible to form the basis of comparison 

 with those taken at some future time ; and this I am now 

 doing. . . . 



"The light of this nebula is so different in intensity 

 that for a proper exposure of the outer portions the cen- 

 tral part is much over-exposed ; it is therefore necessary 

 to take photographs with different exposures. Thus an 

 exposure of from one to three minutes gives the brighter 

 portions of the central parts in such a way that they can 

 be easily compared and their order noted ; longer ex- 

 posures giving portions less bright in a similar way, till, 

 with a m iximum exposure, the very faintest portions can 

 be compared and noted in order. The stars in the nebula 

 can be treated in the same way, the same photographs 

 being available." 



We have before referred to the fact that many of the 

 stars in and about the nebula are variable, particularly 

 the faint ones. Mr. Common has found that one of the 

 brighter stars is remarkably variable, though what its 

 period is he has not yet determined. 



As the time of exposure can be easily extended to 

 hours, it will evidently in the not distant future be easy 

 to get stars invisible to the eye in the same telescope used 

 for photography. 



NOTES 

 Among the gold meda's awarded by the juries of ihe Inter- 

 national Fisheries Exhibition are the following in the depart, 

 ment of Natural History :— Invertebrata.— United Kingdom : 

 James CoDk, the Duke of Edinburgh, Prof. Mcintosh, Thos. 

 Bolton. Italy : Dr. Dohrn (2). Netherlands : Netherlands 

 Zoological Society. United States : United States Fish Com- 

 mission. New South Wales : Sydney Museum. Sweden : 

 F. B. Wittrock, Baron Nordenskjold, W. Lilljeborg. Russia: 

 Dr. Oscar Grimm. Fish, &c — United States : United 

 States National Museum, United States Fish Commission, 

 Prof. Alexr. Agassiz, Prof. G. Brown-Goode, Prof. David S. 

 Jordan. New South Wales : Australian Museum, Sydney (2) ; 

 New South Wales Commisi-ion, Hon. W. Mackay, E. P. Ram- 

 say. Sweden : the Royal Swedish Academy, Dr. Oscar Dickson. 

 Canada : Canadian Government. China : Government of. 



