On Periodic Variations of Terrestrial Magnetism, 395 



riably to rotate in a direction indicating a stream from anode 

 to cathode. Concave aluminium cups are used for both 

 electrodes, and the direction of rotation of the wheel is found 

 immediately to reverse when the positive and negative con- 

 nexions are transposed. 



These experiments consequently confirm the hypothesis 

 suggested in my former paper, that at very high exhaustions 

 there exists a molecular or atomic stream from anode to cathode 

 which carries a positive charge and travels at considerable 

 velocity out«ide of the opposite cathode-stream. 



XL. On the Possible Effects of Solar Magnetization on 

 Periodic Variations of Terrestrial Magnetism. By Arthur 

 Schuster, F.R.S* ' 



1. TX the various attempts which have been made to 



J_ establish a periodicity in the elements of terrestrial 

 magnetism, depending on solar rotation, it has been uni- 

 formly assumed that the periodic time is that of the synodic 

 revolution of the sun. This seems plausible at first sight, 

 but on closer investigation it is found not to be true. 



There are two principal periods which might be caused by 

 a transversely magnetized sun, one being of about 25 days 

 and equal to the time of sidereal revolution, while the other, 

 and more important, has a time of 29*1 days, being longer 

 than the synodical revolution by about as much as that is 

 longer than the sidereal revolution. 



Minor periods are produced by the eccentricity of the 

 earth's orbit, and among these one has a time equal to that of 

 the synodical revolution. But as the amplitude of this period 

 amounts only to about the thousandth part of the amplitude 

 of the principal period, it may for all practical purposes be 

 neglected. 



If it can be proved, therefore, that the elements of terrestrial 

 magnetism have a period equal to that of the synodic revo- 

 lution of the sun, while the sidereal period is absent, it would 

 follow that this cannot be due to a direct effect of solar mag- 

 netization. At present, however, the so-called 26-day period 

 rests on a feeble and altogether insufficient basis, which is still 

 further weakened by the absence of any vera causa for the 

 period. 



The reason why the solar revolution does not produce the 

 effect which is commonly ascribed to it, lies in the fact that 



* Communicated by the Author, 



