. Popular science monthly. culation, and showed that the high potential electric charge demandedby their theory could not possibly exist on the earths surface. It re-mained for Schuster to suggest that a body made up of molecules whichare neutral in the ordinary electrical or magnetic sense may neverthe-less develop magnetic properties when rotated. We shall soon have occasion to examine the two hypotheses ad-vanced in support of this view. While both are promising, it can notbe said that either has been sufficiently developed to explain completelythe principal phenomena of terrestrial magneti
. Popular science monthly. culation, and showed that the high potential electric charge demandedby their theory could not possibly exist on the earths surface. It re-mained for Schuster to suggest that a body made up of molecules whichare neutral in the ordinary electrical or magnetic sense may neverthe-less develop magnetic properties when rotated. We shall soon have occasion to examine the two hypotheses ad-vanced in support of this view. While both are promising, it can notbe said that either has been sufficiently developed to explain completelythe principal phenomena of terrestrial magnetism. If we turn to ex-periment, we find that iron globes, spun at great velocity in the lab-oratory, fail to exhibit magnetic properties. But this can be accountedfor on either hypothesis. What we need is a globe of great size, which 1 Address delivered upon the occasion of the semi-centennial anniversary ofthe foundation of the National Academy of Sciences, April 22, 1913. vol. lxxxiii.—8. io6 THE POPULAR SCIENCE MONTHLY. Fig 1. Dieect Photogeaph of the Sun with Dot representingEaeth foe Comparison. has been rotating for centuries at high velocity. The sun, with a diam-eter one hundred times that of the earth (), may throw some lighton the problem. Its high temperature wholly precludes the existence ofpermanent magnets: hence any magnetism it may exhibit must be dueto motion. Its great mass and rapid linear velocity of rotation shouldproduce a magnetic field much stronger than that of the earth. Finally,the presence in its atmosphere of glowing gases, and the well-knowneffect of magnetism on light, should enable us to explore its magneticfield even at the distance of the earth. The effects of ionization, prob-ably small in the region of high pressure beneath the photosphere andmarked in the solar atmosphere, must be determined and allowed with this important limitation, the sun may be used by the physi-cist for an experiment which can not be performed in the best
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