158 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1913. 



In this survey of magnetic phenomena we have kept constantly 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, could not exist at the high temperature 

 of the sun. Displays of the aurora, usually accompanied by mag- 

 netic storms, are plausibly attributed to electrons reaching the earth 

 from the sun, and illuminating the rare gases of the upper atmos- 

 phere 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 magnetic 

 intensity is sometimes as great as nine thousand times that of the 

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

 lution in a vortex of negative electrons, flowing toward the cooler 

 spot from the hotter region outside. The same method of observa- 

 tion 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 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 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 fm^ther 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. 



