THE EARTH AND SUN AS MAGNETS 115 



Fig. 9. Zeexian Doublet ruoTOGKAPHED in Labokatoky SrEcruu.M. The middle 

 section shows the doublet. The adjacent sections indicate the appearance of the 

 spectrum line in the absence of a magnetic field. 



site directions. With suitable polarizing apparatus, either component of 

 such a line can be cut off at will, leaving the other unchanged. Further- 

 more, a double line having these characteristic properties can be pro- 

 duced only by a magnetic field. Thus it becomes a simple matter to 

 detect a magnetic field, at any distance, by observing its effect on light 

 emitted within the field. If a sun-spot is an electric vortex, and the 

 observer is supposed to look along the axis of the whirling vapor, which 

 would correspond with the direction of the lines of force, he should find 

 the spectrum lines double, and be able to cut off either component with 

 the polarizing attachment of his spectroscope. 



I applied this test to sun-spots on Mount AVilson in June, 1908, 

 with the 60-foot tower telescope, and at once found all of the charac- 

 teristic features of the Zeeman effect. Most of the lines of the sun- 

 spot spectrum are merely widened by the magnetic field, but others are 

 split into separate components (Fig. 10), which can be cut off at will by 

 the observer. ^Moreover, the opportune formation of two large spots, 

 which appeared on the spectroheliograph plates to be rotating in oppo- 

 site directions (Fig. 11), permitted a still more exacting experiment to 

 be tried. In the laboratory, where the polarizing apparatus is so ad- 

 justed as to transmit one component of a line doubled by a magnetic 

 field, this disappears and is replaced by the other component when the 

 direction of the current is reversed. In other words, one component is 

 visible alone when the observer looks toward the north pole of the 

 magnet, while the other appears alone when he looks toward the south 

 pole. If electrons of the same kind are rotating in opposite directions 

 in two sun-spot vortices, the observer should be looking toward a north 

 pole in one spot and toward a south pole in the other. Hence the 



