Masterpieces of Science 



In passing from the colours of the solar spec- 

 trum to its many minute interruptions, "the new 

 astronomy" began. As photographed by Pro- 

 fessor Rowland upon sheet after sheet for a total 

 length of forty feet, the spectrum of the sun is 

 crossed by thousands of dark lines. The inter- 

 pretation of the most conspicuous of these lines 

 by Bunsen and Kirchhoff in 1859, marks an epoch 

 in the study of the heavens. Let us approach 

 their explanation by a simple experiment. If we 

 sing a certain note upon the wires of an open 

 piano, just that strinp; will respond which, if it 

 were struck, would utter that note. Precisely 

 so when we pass from vibrations of sound to those 

 of light; a vapour when cool absorbs by sym- 

 pathy those waves of light which, if it were highly 

 heated, it would send forth. Hence the dark 

 lines in the solar spectrum tell us what particular 

 gases, at comparatively low temperatures, are 

 stretched as an absorbing curtain between the 

 inner blazing core and outer space. To choose 

 a convincing example: when the spectrum of the 

 sun and that of iron are compared side by side 

 in the same instrument, bright lines of the iron 

 coincide with dark lines of the solar spectrum. 



The tints and lines of a spectrum, whether from 

 the sun or a star, disclose not only the character 

 but the consistence of the elements which send 

 them to the eye or to the photographic plate. 

 Hydrogen, for example, when it burns at ordinary 

 pressures, as it may in the simplest laboratory 

 experiment, emits a spectrum of bright lines 



