THE MICROSCOPE. 115 



and more indispensable as a means of scientific research, The 

 chemically prepared film of the photographic plate is capable 

 of recording faint markings and minute structural details, 

 which cannot be detected in the microscopic image by the 

 human eye, or at least very imperfectly. As an illustration of 

 this, from an astronomical point of view, the following facts 

 with respect to the discovery of small planetary bodies which 

 move in orbits between those of Mars and Jupiter may be in- 

 teresting : — "From observations of the first of these, Ceres, in 

 1801 until the end of 1891, 321 had been discovered by the 

 comparatively laborious method of eye observation. From 

 that time photography has been pressed into the service, and 

 no fewer than 44 have been found within the last fifteen 

 months. Professor Charlois, of Nice, reports the finding of 

 six during the last week, a feat which would have been con- 

 sidered unparalleled at the beginning of the century." This I 

 think conclusively proves the superiority of photography in 

 special work of this kind. The above is only one of the many 

 applications of photography for recording astronomical phe- 

 nomena, all of which have been of great service. 



It is equally applicable to microscopical investigations; and 

 a much more correct idea of the structure or the nature of the 

 markings in various minute organisms, has been gained by 

 its use, than could have been arrived at by eye observation 

 alone, notably the spendid photo-micrographs of some of the 

 Diatomacere, which have been taken with the most perfect 

 and most powerful objectives made. It is impossible to pre- 

 dict to what extent the aid of photography will be found use- 

 ful in deciding obscure physiological questions. 



Professor Exmer, of Vienna, has succeeded in taking the 

 photomicrograph of the image which is formed at the back of 

 the compound eye of an insect. This image he found to be 

 precisely the same as that which would be presented at the 

 back of the single eye of one of the higher vertebrates. As 

 the physiology of the arthropod eye has been the subject of 

 much discussion and diversity of opinion, this discover}^ may 

 be the means of throwing a new light on the question, and, if 

 so, it will be another of the triumphs of photography in eluci- 

 dating this and similar phenomena. 



