IIST TIIE LAST HALF-CENTURY. 103 



heat proceeding from different sources by 

 solid, fluid, and gaseous bodies. And it 

 is a curious example of the interconnec- 

 tion of the various branches of physical 

 science, that some of the results thus ob- 

 tained have proved of great importance in 

 meteorology. 



The existence of numerous dark lines, 

 constant in their number and position in 

 the various regions of the solar spectrum, 

 was made out by Fraunhofer in the early 

 part of the present century, but more than 

 forty years elapsed before their causes 

 were ascertained and their importance rec- 

 ognised. Spectroscopy, which then took 

 its rise, is probably that employment of 

 physical knowledge, already won, as a 

 means of further acquisition, which most 

 impresses the imagination. For it has The 

 suddenly and immensely enlarged our scope. 

 power of overcoming the obstacles which 

 almost infinite minuteness on the one 

 hand, and almost infinite distance on the 



