348 THE WORLD MACHINE 



Latterly the camera has proved a wonderful aid. Instead 

 of trusting merely to the momentary impressions of the eye, 

 it is possible to photograph the varying spectra with accuracy ; 

 moreover, to follow the spectrum out beyond the range of the 

 eye into the so-called ultra-violet portions, whose rays affect 

 only photographic plates. These spectrograms make possible 

 measures and comparisons which would be quite impossible to 

 the unaided eye. Likewise they may be copied and sent about 

 from one worker to another, so that results may be discussed 

 at first-hand by various minds. 



The fact of largest philosophic interest which we owe to 

 the spectroscope is the demonstration that the material of the 

 solar system and of the universe as well is all the same. This 

 had been long surmised ; obviously it could be only a con- 

 jecture. Of the seventy odd elements known upon the earth, 

 many show their characteristic lines in the spectrum of the 

 sun. Not all ; and this has led to the idea that perhaps in 

 the enormous temperatures of the sun our so-called elementary 

 atoms are decomposed, disassociated into a comparatively few 

 simpler forms. 



On the other hand, practically all of the solar lines could be 

 accounted for. There were a few outstanding. They seemed 

 unmistakably to indicate the existence of substances which no 

 terrestrial chemist had ever seen. It is the essence of true theory 

 that it shall, if need be, afford the basis of prediction. Spite of 

 all the bizarre tracings with which he had to deal, the spectro- 

 scopist did not hesitate. He announced new elements, gave 

 them a name; he even hazarded a guess at their nature and 

 their place in the chemic scale. 



So commonplace has all this become that it does not now 

 seem bold ; quite the contrary. So closely interlinked are the 

 physical investigations of to-day that what once seemed daring 

 now appears merely a necessary consequence. It is the difference 

 of the times. The predictions of the spectroscopist, it hardly 

 needs be said, were subsequently verified, most notably by the 

 discovery of the hypothetical element, helium, which does not 

 belong to the sun alone, but to the earth as well. 



As the study advanced it became further evident that the 

 spacing of the spectral lines is influenced by the temperature 

 of the body from which the light comes ; if it be a gas, it is 

 influenced by the pressure. In following out these and similar 



