i2 4 THE POPULAR SCIENCE MONTHLY 



The lines which show the Zeeman effect originate at a comparatively 

 low level in the solar atmosphere. Preliminary measures indicate that 

 certain lines of titanium, which are widely separated by a magnetic 

 field in the laboratory, are not appreciably affected in the sun. As 

 these lines represent a somewhat higher level, it is probable that the 

 strength of the sun's field decreases very rapidly in passing upward 

 from the surface of the photosphere — a conclusion in harmony with 

 results obtained from the study of the corona and prominences. Thus 

 it may be found that the distribution of the electrons is such as to give 

 rise to the observed field or to produce a field opposing that caused by 

 the rotation of the body of the sun. It is evident that speculation 

 along these lines may advantageously await the accumulation of ob- 

 servations covering a wide range of level. Beneath the photosphere, 

 where the pressure is high, we may conclude from recent electric fur- 

 nace experiments by King that free electrons, though relatively few, 

 may nevertheless play some part in the production of the general mag- 

 netic field. 



In this smvey of magnetic phenomena, we have kept constantly in 

 mind the hypothesis that the magnetism of the earth is due to its rota- 

 tion. Permanent magnets, formerly supposed to account for the earth's 

 magnetic field, could not exist at the high temperature of the sun. 

 Displays of the aurora, usually accompanied by magnetic storms, are 

 plausibly attributed to electrons reaching the earth from the sun, and 

 illuminating the rare gases of the upper atmosphere just as they affect 

 those in a vacuum tube. Definite proof of the existence of free elec- 

 trons in the sun is afforded by the discovery of powerful local magnetic 

 fields in sun-spots, where the magnetic intensity is sometimes as great 

 .-as nine thousand times that of the earth's field. These local fields 

 ■probably result from the rapid revolution in a vortex of negative elec- 

 trons, flowing toward the cooler spot from the hotter region outside. 

 'The same method of observation now indicates that the whole sun is a 

 magnet, of the same polarity as the earth. Because of the high solar 

 temperature, this magnetism may be ascribed to the sun's axial rota- 

 tion. 5 It is not improbable that the earth's magnetism also results 

 from its rotation, and that other rotating celestial bodies, such as stars 

 and nebulas, may ultimately be found to possess magnetic properties. 

 Thus, while the presence of free electrons in the sun prevents our 

 acceptance of the evidence as a proof that every large rotating body is 

 a magnet, the results of the investigation are not opposed to this 

 hypothesis, which may be tested further by the study of other stars of 

 known diameter and velocity of rotation. 



B The alternative hypothesis, that the sun 's magnetism is due to the com- 

 bined effect of numberless local magnetic fields, caused by electric vortices in 

 the solar ' ' pores, ' ' though at first sight improbable, deserves further con- 

 sideration. 



