156 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 8 



significantly that such discharges in the upper atmosphere are indeed 

 the result of bombardments of electrons coming in from outside, 

 warped by the magnetic field of the earth. In endeavoring to express 

 such phenomena on an electronic hypothesis we may well look at the 

 sun, therefore, for a consideration of the character of sunspots and 

 to trace any possible mechanism by which corpuscular charges might 

 be ejected in the regions of the sunspots themselves. 



When we look at an enlarged view of a sunspot and analyze the 

 light from it we find that the dark interior center is surrounded by a 

 turbulent area. A photograph taken in the light emitted by hydrogen 

 at one particular frequency reveals that here are whirling masses of 

 gas, arranging themselves in veritable vortices. There is every indi- 

 cation, then, that a sunspot is in reality a terrific solar hurricane. It 

 was in 1908 that the late Dr. George Ellery Hale, the founder and 

 director of the Mount Wilson Observatory, first observed that sun- 

 spots were giant cyclones in the sun's atmosphere. They are indeed 

 very similar in their formation to the tropical hurricanes that originate 

 in the West Indies and sweep northward. 



An ordinary telescope would never have disclosed all this about 

 sunspots. With a special contrivance of his own invention called the 

 spectroheliograph he was able to photograph the sun, utilizing the 

 light of a given frequency from one chemical element at a time. The 

 spectroheliograph is a sort of a combination of a spectroscope and a 

 moving plate arrangement, somewhat similar to a motion picture 

 outfit in its operation. With this device it is possible to photograph 

 the distribution of clouds of chemicals whose presence in the sun's 

 atmosphere is betrayed by the lines in the spectrum. Since the 

 invention of the spectroscope it has been known that hydrogen and 

 calcium, for example, are very conspicuous elements entering into 

 the sun's makeup. 



With photographic emulsions made especially sensitive to the red 

 light emitted by hydrogen Dr. Hale photographed on a moving film 

 the entire solar surface so far as it was covered by bright luminous 

 hydrogen clouds. The resulting representations of the sun appeared 

 very different from photographs made in ordinary light. Not only 

 were large clouds of hydrogen gas discernible all over the sun, but in 

 the neighborhood of sunspots they seemed to be swept into the heart of 

 the spot as though they were caught in the center of a whirlpool. 

 Pictures of sunspots taken in this way show the same kind of vortex 

 as one often sees when a basin is being emptied of water by the sudden 

 removal of a drain plug at the bottom of the bowl. Such an appear- 

 ance might be presented by the top of a terrestrial cyclone or tornado 

 if photographed from a stratospheric balloon. The dark center of the 

 spot forms the center of the vortex; the outlying shaded region that 

 characterizes the so-called penumbra of the sunspot would represent 



