X THE STARRY HEAVENS 385 



possibility of our existence, we are indebted 

 to the Sun. 



What is the Sun made of ? Comte men- 

 tioned as a problem, which it was impossible 

 that man could ever solve, any attempt to 

 determine the chemical composition of the 

 heavenly bodies. " Nous concevons," he said, 

 " la possibility de determiner leurs formes, 

 leurs distances, leurs grandeurs, et leurs mouve- 

 ments, tandis que nous ne saurions jamais 

 etudier par aucun moyen leur composition 

 chimique ou leur structure min^ralogique." 

 To do so might well have seemed hopeless, 

 and yet the possibility has been proved, and a 

 beginning has been made. In the early part 

 of this century Wollaston observed that the 

 bright band of colours thrown by a prism, and 

 known as the spectrum, was traversed by 

 dark lines, which were also discovered, and 

 described more in detail, by Fraunhofer, after 

 whom they are generally called " Fraunhofer's 

 lines." The next step was made by Wheat- 

 stone, who showed that the spectrum formed 

 by incandescent vapours was formed of bright 

 lines, which difEered for each substance, and 



2c 



