THE SUN AND THE ATMOSPHERE STETSON 157 



the turbulence bordering upon the central funnel about which the 

 atmospheric particles are rapidly rotating. Thus we see there is a 

 close analogy between the meteorology of tropical cyclones and that 

 of sunspots. To carry the analogy still further, spots north of the 

 sun's equator are in general whirling in one direction while corre- 

 sponding spots south of the equator whirl in the opposite direction. 

 If the rotation of the one is clockwise, that of the other is counter- 

 clockwise. This again is characteristic of the differences of rotation 

 of tropical hurricanes on the earth originating in the northern and 

 southern hemispheres, respectively. 



Had it not been for the trick of splitting up sunlight into isolated 

 frequencies by means of the spectroscope, we should never have had 

 pictures showing the existence of solar vortices such as we have today. 

 In the ordinary photograph of the sun, the light emitted by every 

 chemical element in the sun's atmosphere is clamoring to tell its 

 story. The result is revealed in a rather jumbled picture of what is 

 happening on the sun. The spots show up as dark regions only when 

 the light-emitting power of every element of the sun is damaged in 

 the vicinity of these violently disturbed regions. 



The spectroscope is very much like a highly selective radio receiving 

 set. The sun is a high-powered station sending out light, broadcast 

 in all the wave lengths and frequencies. When we look at the sun 

 or photograph it with a telescope alone, we are using all of the light 

 and are, so to speak, operating a radio receiver which admits all fre- 

 quencies at once. Thus we get a composite but very jumbled picture 

 of what is happening on the sun's surface so far as details are con- 

 cerned. By means of the spectroscope, however, the photographic 

 apparatus, to continue our analogy, may be tuned to a single fre- 

 quency such as the 470 million megacycle frequency that the red line 

 of hydrogen emits. Tuned to this frequency, the spectroscope stills 

 the tumult of all other elements and lets hydrogen tell its own story. 

 It is then that we obtain the clear photographs conveying so beauti- 

 fully the detailed information about the vortical whirls around the 

 solar storm centers that would otherwise be lost in the jumble of too 

 many story-tellers. 



At about the same time another brilliant discovery due to Dr. 

 Hale came from the Mount Wilson Observatory. It had long been 

 known that the frequencies of light waves were distorted if there were 

 a powerful magnetic field at the light source. This had been demon- 

 strated in the laboratory shortly after the reason for such a phenomenon 

 had been given by Zeeman in 1894. When the Mount Wilson ob- 

 servers examined and actually measured the frequency of light coming 

 from the centers of simspots, it was found to have changed frequency 

 in exactly the way that light waves are distorted in the laboratory 

 when a powerful electromagnet is placed around the source of light 



