H THE PROGRESS OF SCIENCE 111 



paper and glass for the silvered plates then in use. 

 It is not my affair to dwell upon the practical 

 application of the photography of the present day, 

 but it is germane to my purpose to remark that 

 it has furnished a most valuable accessory to the 

 methods of recording motions and lapse of time 

 already in existence. In the hands of the 

 astronomer and the meteorologist, it has yielded 

 means of registering terrestrial, solar, planetary, 

 and stellar phenomena, independent of the sources 

 of error attendant on ordinary observation ; in the 

 hands of the physicist, not only does it record 

 spectroscopic phenomena with unsurpassable ease 

 and precision, but it has revealed the existence of 

 rays having powerful chemical energy, or beyond 

 the visible limits of either end of the spectrum ; 

 while, to the naturalist, it furnishes the means by 

 which the forms of many highly complicated 

 objects may be represented, without that 

 possibility of error which is inherent in the work 

 of the draughtsman. In fact, in many cases, the 

 stern impartiality of photography is an objection 

 to its employment : it makes no distinction 

 between the important and the unimportant ; and 

 hence photographs of dissections, for example, are 

 rarely so useful as the work of a draughtsman 

 who is at once accurate and intelligent. 



The determination of the existence of a new 

 planet, Neptune, far beyond the previously known 

 bounds of the solar system, by mathematical 



