54 NATIONAL ACADEMY OF SCIENCES 



along these lines may advantageously await the accumulation 

 of observations covering a wide range of level. Beneath the 

 photosphere, where the pressure is high, we may conclude from 

 recent electric furnace experiments by King that free electrons, 

 though relatively few, may nevertheless play some part in the 

 production of the general magnetic field. 



In this survey of magnetic phenomena, we have kept con- 

 stantly in mind the hypothesis that the magnetism of the earth 

 is due to its rotation. Permanent magnets, formerly supposed 

 to account for the earth's magnetic field, probably can 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 electrons 

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

 fields in sun-spots, where the intensity of the field is sometimes as 

 great as nine thousand times that of the average value of the 

 earth's field. These local fields probably result from the rapid 

 revolution in a vortex of negative electrons, 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 tempera- 

 ture, this magnetism may be ascribed to the sun's axial rotation.* 

 It is not improbable that the earth's magnetism also results from 

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

 and nebulae, may ultimately be found to possess magnetic prop- 

 erties. Thus, while the presence of free electrons in the sun pre- 

 vents 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. 



* The alternative hypothesis, that the sun's magnetism is due to the combined effect of 

 numberless local magnetic fields, caused by electric vortices in the solar " pores," though at 

 first sight improbable, deserves further consideration. 



