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THE POPULAR SCIENCE MONTHLY 



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. 



Thus we were led to the hypothesis that sun-spots are closely anal- 

 ogous to tornadoes or water-spouts in the earth's atmosphere (Fig. 8). 



Fig. 8. Water-spout. 



If this were true, electrons, caugbt and whirled in the spot vortex, 

 should produce a magnetic field. Fortunately, this could be put to a 

 conclusive test, through the well-known influence of magnetism on light 

 discovered by Zeeman in 1896. 



In Zeeman's experiment a flame containing sodium vapor was placed 

 between the poles of a powerful electro-magnet. The two yellow sodium 

 lines, observed with a spectroscope of high dispersion, were seen to widen 

 the instant a magnetic field was produced by passing a current through 

 the coils of the magnet. It was subsequently found that most of the 

 lines of the spectrum, which are single under ordinal y conditions, are 

 split into three components when the radiating source is in a sufficiently 

 intense magnetic field. This is the case when the observation is made 

 at right angles to the lines of force. When looking along the lines of 

 force, the central line of such a triplet disappears (Fig. 9), and the light 

 of the two side components is found to be circularly polarized in oppo- 



