512 POPULAR LECTURES AND ADDRESSES. 



terrestrial magnetism is a necessary consequence of 

 the magnitude and the rotation of the earth, other 

 bodies comparable in these qualities with the earth, 

 and comparable also with the earth in respect to 

 material and temperature, such as Venus and 

 Mars, must be magnets comparable in strength 

 with the terrestrial magnet, and they must have 

 poles similar to the earth's north and south poles 

 on the north and south sides of their equators, 

 because their directions of rotation, as seen from 

 the north side of the ecliptic, are the same as that 

 of the earth. It seems probable, also, that the 

 sun, because of its great mass and its rotation in 

 the same direction as the earth's rotation, is a 

 magnet with polarities on the north and south 

 sides of its equator, similar to the terrestrial 

 northern and southern magnetic polarities. As 

 the sun's equatorial surface-velocity is nearly four 

 and a half times the earth's, it seems probable that 

 the average solar magnetic moment exceeds the 

 terrestrial considerably more than according 

 to the proportion of bulk. Absolutely ignor- 

 ant as we arc regarding the effect of cold 



