x THE STAKRY 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 possibilite 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 mineralogique." 

 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 differed for each substance, and 



2c 



