science. 



110 THE ADVANCE OF SCIENCE 



ly into the penetralia of nature, as does 

 the sense of sight. 

 Photog- That light exerts a remarkable influ- 

 as a/ ence in bringing about certain chemical 

 mentof combinations and decompositions was well 

 known fifty years ago, and various more 

 or less successful attempts to produce 

 permanent pictures, by the help of that 

 knowledge, had already been made. It 

 was not till 1839, however, that practical 

 success was obtained ; but the ' daguerre- 

 otypes ' were both cumbrous and costly, 

 and photography would never have at- 

 tained its present important development 

 had not the progress of invention substi- 

 tuted paper and glass for the silvered 

 jDlates 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 ac- 

 cessory to the methods of recording mo- 

 tions and lapse of time already in exist- 



