Variation Phenomenon of Terrestrial Magnetism. 501 



and knowing the amount in time of the retardation of the 

 inner sphere for a complete rotation of the outer, the secular 

 variation at any point could be ground out. 



It will be seen that Wilde has presented us with a totally 

 different idea in his mechanism from that of his theory. His 

 theory would have the internal sphere differentially rotating 

 about its axis of magnetization with the plane of rotation 

 parallel to that of the ecliptic. Nothing whatever is said as to 

 its transportation about the terrestrial axis, as a whole. Hence, 

 the magnetic pole would be a transient one and be induced 

 successively on every meridian during the diurnal rotation of 

 the terrestrial shell, and the maximum effect would appear in 

 the diurnal variation of the needle and not in the secular. 

 But we know that the former is but a small percentage of the 

 latter, hence it must be evident that Wilde has not given us 

 his whole theory. Are we to suppose that the gaseous sphere 

 rotates about an axis which itself rotates about the terrestrial 

 axis and is thus continually changing its plane of rotation dur- 

 ing every twenty-four hours ? Only in this way could a 

 permanent pole be maintained. 



In his mecha?iism he has the inner sphere differentially 

 rotating about the axis of the outer with its axis of magneti- 

 zation inclined to it at an angle of 23 "5 degrees. This certainly 

 simplifies the physical conditions. But are we to suppose that 

 w T hen the plane of rotation of the inner sphere gradually 

 changed its primitive direction until it coincided with the 

 outer one, the axis of magnetization of this vaporous sphere 

 was so rigid that it remained fixed ? Is it possible that Wilde 

 wishes us to understand that the circulation of currents of 

 electricity round the inner sphere is equivalent to a rotation of 

 the sphere? 



The first point made in this paper, then, is that Wilde's 

 mechanism does not coincide with his theory as he has given 

 it to us. 



But now let us set aside all discussion as to the theory and 

 the physical conditions involved and discuss the results from 

 the standpoint of Terrestrial Magnetism alone, Were it 

 necessary for the support of the argument to arrive at the 

 probable error of the magnetarium results, among others, the 

 following points might be mentioned which would affect them 

 and in regard to which Wilde says nothing. 



(1.) The effect on the needles by the earth's magnetic force 

 at the station where the results are ground out. 



(2.) The sensible amount, his needles being in proportion to 

 the diameter of the outer sphere as 1 : 9, by which they would 

 be attracted directly or obliquely towards that globe as the 



