FREE INSTITUTE OF SCIENCE ^^ 



ETHER WAVES AND THE MESSAGES THEY BRING 



of any substance known to exist on the earth. Since these lines are formed by 

 the absorption of certain wave lengths from light which would form a con- 

 tinuous spectrum, it is possible, by a study of them, to tell what gases the Hght 

 has passed through. On the screen you see a part of the solar spectrum super- 

 imposed upon the spectrum of iron vapor (Fig. 2). You will note that the 

 coincidence of the bright lines of the vapor spectrum with the dark lines of the 

 solar spectrum is perfect. This seems to be positive evidence that the vapor of 

 iron is present in the sun's atmosphere. Kirchhoff has shown that the coinci- 

 dence is complete for the 460 bright lines known to exist in the spectrum of iron 

 vapor. It might be thought that the coincidence is merely chance, since such 

 a large number of these lines exist in the spectrum of the sun. Kirchhoff cal- 

 culated that the odds against mere chance in the matter are a million million 

 milUons to one. By the same method a great many elements have been dis- 

 covered in the sun, among them H, Fe, Ca, He, Mg, Ni, Zn, and Cu. It might 



Fig. 2. — Solar spectrum with superimposed iron spectrum. 



be noted that Au, As, Hg, N, and S are some of the common ones found on the 

 earth which have not been found there. 



In the same way the Hght of the stars has been studied and much interest- 

 ing information gathered concerning the elements of which they are composed. 



But this is only the beginning of the statement of the interesting facts 

 concerning celestial bodies which these ether waves bring to us. To under- 

 stand fully some others it is necessary to discuss at this point a principle in 

 wave motion known as Doppler's principle. 



In the upper Hne of the diagram on the screen (Fig. 3, A), let us suppose 

 an observer stationed at A while a body producing waves is at 5. We will 

 suppose that the body produces ten waves per second, and that the distance 

 A Bis numerically equal to the speed of the waves expressed in units per second. 

 Then at the end of one second the first wave will have reached the observer 

 and the tenth wave will have just been produced at B. The distance between 



