44 NATIONAL ACADEMY OF SCIENCES 



net to a red heat, it loses its magnetism, and drops the iron bar 

 which it previously supported. Hence, while some theories 

 attribute terrestrial magnetism to the presence within the earth 

 of permanent magnets, no such theory is likely to apply to the 

 sun. If magnetic phenomena are to be found there, they must 

 result from other causes so far as we can judge from our present 

 knowledge of magnetic phenomena at high temperatures. 



The familiar case of the helix illustrates how a magnetic field 

 is produced by an electric current flowing through a coil of wire. 

 But according to the modern theory, an electric current is a 

 stream of electrons. Thus a stream of electrons in the sun should 

 give rise to a magnetic field. If the electrons were whirled in a 

 powerful vortex, resembling our tornadoes or water-spouts, the 

 analogy with the wire helix would be exact, and the magnetic 

 field might be sufficiently intense to be detected by spectroscopic 

 observations. 



A sun-spot, as seen with a telescope or photographed in the 

 ordinary way, does not appear to be a vortex. If we examine the 

 solar atmosphere above and about the spots, we find extensive 

 clouds of luminous calcium vapor, invisible to the eye, but easily 

 photographed with the spectroheliograph, by admitting no light 

 to the sensitive plate except that radiated by calcium vapor. 

 These calcium flocculi (Fig. 5), like the cumulus clouds of the 

 earth's atmosphere, exhibit no well-defined linear structure. But 

 if we photograph the sun with the red light of hydrogen, we 

 find a very different condition of affairs (Fig. 6) . In this higher 

 region of the solar atmosphere, first photographed on Mount 

 Wilson in 1908, cyclonic whirls, centering in sun-spots, are 

 clearly shown. 



The idea that sun-spots may be solar tornadoes, which was 

 strongly suggested by such photographs, soon received striking 

 confirmation. A great cloud of hydrogen, which had hung for 

 several days on the edge of one of these vortex structures, was 

 suddenly swept into the spot at a velocity of about 60 miles per 

 second. More recently Slocum has photographed at the Yerkes 

 Observatory a prominence at the edge of the sun, flowing into 

 a spot with a somewhat lower velocity. 



