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 possibilité de déterminer leurs formes, 
leurs distances, leurs grandeurs, et leurs mouve- 
ments, tandis que nous ne saurions jamais 
étudier par aucun moyen leur composition 
chimique ou leur structure minéralogique.” 
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 
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