Masterpieces of Science 



The telescope, then is essentially a light- 

 gatherer. 



The spectroscope is used for another purpose. 

 It might be called the light-sifter. It is applied 

 by the astronomer to analyze the light which 

 comes to him from beyond the ocean of space, 

 and so to enable him to learn the character of 

 the orbs from which that light proceeds. 



The principle of the instrument is simple, 

 though the appliances by which its full powers 

 can alone be educed are somewhat complicated. 



A ray of sunlight falling on a prism of glass 

 or crystal does not emerge unchanged in charac- 

 ter. Different portions of the ray are differently 

 bent, so that when they emerge from the prism 

 they no longer travel side by side as they did 

 before. The violet part of the light is bent most, 

 the red least; the various colours from violet 

 through blue, green and yellow, to red, being 

 gradually bent less and less. 



The prism then sorts, or sifts, the light-waves. 



But we want the means of sifting the light- 

 waves more thoroughly. The reader must bear 

 with me while I describe, as exactly as possible in 

 the brief space available to me, the way in which 

 the first rough work of the prism has been mod- 

 ified into the delicate and significant work of the 

 spectroscope. It is well worth while to form 

 clear views on this point, because so many of the 

 wonders of modern science are associated with 

 sp^ctroscopic analysis. 



If, through a small round hole in a shutter, 

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