evidence, open to only one interpretation, proved 

 the existence of magnetic fields in sun-spots, and 

 strengthened the view that these are caused by 

 electric vortices. This conclusion, in common 

 with many others regarding the nature of sun- 

 spots, could not have been obtained without the 

 aid of the physical laboratory. 



A B 



I I 



i 



1 1 



a 

 b 

 a 

 b 

 a 



FIG. 22. Effect of Nicol and Compound Quarter-wave Plate upon (-4) 

 Lines of Spark in Magnetic Field and (B) Solar Line in Spectrum 

 of Sun-spot, a Red Components; b Violet Components; middle 

 line of Triplet shows in B but not in A. 



Let us see how the effect of magnetism on light 

 is studied. We place our iron arc or spark between 

 the poles of a powerful magnet (Fig. 29) and pho- 

 tograph its spectrum. The lines behave in the most 

 diverse way, some splitting into triplets, others into 

 quadruplets, quintuplets, sextuplets, etc. One 

 chromium line is resolved by the magnet into 21 



