gg TRANSACTIONS OF WAGNER 



ETHER WAVES AND THE MESSAGES THEY BRING 



hydrogen line, the hydrogen areas of the sun will be photographed, and so for 

 any gas whatever. Now this method of study has led for the first time to an 

 accurate knowledge of the distribution of gases in the atmosphere of the sun, 

 particularly of the enormous quantities of hydrogen and calcium in the regions 

 about sun spots. Also by this method it has been determined just what are 

 the gases forming the gigantic flames shooting out from the sun's orb. These 

 formerly were studied only at times of eclipse, when they were visible as promi- 

 nences on the perimeter of the disk. Now they can be studied and photo- 

 graphed on the face of the disk at any time. Ordinarily the light of the orb 

 is much too briUiant for them to be detected, but by the spectroheliograph all 

 other light except just the wave length to be studied is eliminated. 



It is found in the laboratory that most gases, while they produce per- 

 fectly characteristic spectra, will, under certain conditions of temperature, 

 pressure, and electric potential, produce lines which otherwise are extremely 

 weak or perhaps entirely lacking. For instance, if calcium vapor is dense and 

 hot, a certain line close to the K line comes out strongly; while if it is com- 

 paratively rare and cool, this line is missing. By setting the second slit of the 

 spectroheHograph in this line we get a picture of the sun's atmosphere at a 

 lower level than if we were to select a line which represents the gas at a lower 

 temperature and pressure, for it is clear that the gases become rarer and cooler 

 as we approach the upper layers of the sun's atmosphere. The same reasoning 

 applies to the spectroheliograph pictures made in the lines of any other gas 

 which shows the same behavior, e. g., hydrogen. In this way it is possible to 

 explore the atmosphere of the sun at different levels — a truly marvelous 

 achievement. 



Thus we see that light brings to us the knowledge of many facts besides 

 those which it reveals directly to the eye. Now let us consider briefly some of 

 the other sorts of ether waves. 



If, when a beam of sunlight is dispersed by a prism, we place a thermometer 

 or a thermopyle just beyond the red end of the visible spectrum, we discover 

 that the temperature is higher in this region than on other portions of the 

 screen. This is explained by the statement that in sunlight there exist waves 

 longer than any of those that affect the eye. These longer waves give rise to 

 heat energy when they are intercepted by the screen, or in fact by any body 

 which is not transparent to them. Closer study reveals the fact that all 

 bodies, even at ordinary temperatures, are giving off similar waves, but probably 



