27 



higher part of the hydrogen atmosphere, thus 

 revealed in projection against the disk, immense 

 vortices were found surrounding sun-spots (Fig. 1 8) . 

 This led to the hypothesis that a sun-spot is a solar 

 storm, resembling a terrestrial tornado, in which 

 the hot vapors, whirling at high velocity, are 

 cooled by expansion, thus accounting for the 



FIG. 20. 3O-foot Spectrograph, with Polarizing Apparatus above Slit. 



observed intensity changes of the spectrum lines 

 and the presence of chemical compounds. 



But the observed widening of many spot lines 

 and the doubling or trebling of some of them re- 

 mained inexplicable until the vortex hypothesis 

 suggested an explanation. Thomson and others 

 had shown that electrons are emitted by hot bodies; 

 hence they must be present in great numbers in 



