PHOTOGRAPHY IN ASTRONOMICAL RESEARCH. 178 



even the spectrum of this faint object has been photographed. "Wlien 

 we consider that in tjie spectrum each point of liifht in the object is 

 enormously dihited by being spread out into a Hue, the difliculty of 

 this undertaking seemed almost prohibitive; but it was not sufficient 

 to prevent Mr. Peri'ine, of the Lick Observatory, fi'om making the 

 attemj>t, and ho was deservedly rewarded by success. I may be 

 wrong in regarding this success as the high-water mark iu tliis direc- 

 tion at the i)resent time, and it will prol»ably be suri)assed by some 

 new achievement very shortly; l)ut it will serve to iliusti-ate the 

 power of photogra})hy in dealing with faint objects. 



But may we here pause for one moment to marvel at tlie sensi- 

 tiveness of the human eye. which is such that it is, after all, not 

 left very far behind in the race^ The eye, sensitive as it i^ merely 

 to transient impressions, is no match ultimately for the j)late, which 

 can act by accunnilation. But with similar instruments the plate 

 must be exposed for minutes or even hours to seize the impression 

 of a faint object which the eye can detect at a glance. There seems 

 to be no reason in the nature of things why the eye should not have 

 been surpassed in a few seconds; and in the futui'e the sensitiveness 

 of plates may be increased so that this will actually be the case, even 

 as in the past there was a time when the sensitiveness was so small 

 that the longest ex])osure could not compete with the eye. But this 

 time is not yet come, and at the ])resent moment the eye is still in 

 some departments superior to its rival, owing to this very fact, 

 that though it can only see by glances, it can use these glances to good 

 effect. In the study of the planets the more clumsy method of the 

 photographic plate (which, l)y requiring time for the formation of 

 the image, confuses good moments with bad) renders it almost use- 

 less as compared with the eye; and again, we have not as yet used 

 photography for daylight observations of stars. 



But there is another direction in which the i)h()tographic plate is 

 immensely superior to the eye in power; it can record so much moi-e 

 at once." In. the able hands of Professor Barnard, Dr. Max Wolf, 



a This proporty lias been betuitifiilly illustrated l)y a lecture experiment of 

 Professor P.aruard. He throws on the screen a jiieture of a lar^e nel)nla 

 which the photograi)lii(* plate has no dltHcnlty in jiortraying all at once: hut 

 the picture is, in the Hrst instance, covered up liy a screen, excejjt for ;i suimII 

 ajjerture only, and this aperture, he tells liis audienc<', represents all thai can 

 bo seen by the eye at one time, using tlie iudant telesco])e of the Yerkes Observ.a- 

 tory By movini; tlie screini about, diflereiit jiortions of tlie picture m;iy be 

 viewed siiccessively, as also by moviiiLX the telescope about in lookin.i; at the sky 

 itself. But what a revelation follows wlien 1lu> screen is removed and the full 

 j^lory of the nebula is exiiibited at a sinicle f^lance! We can well understand 

 that the true character ol these objects was hopelessly misinterpreted I)y the 

 eye using the imiierfect method of piecemeal observation, which aloni' was 

 formerly possible. 



