202 MAGNETISM 



added to, or subtracted from, the bundle. For an addition of 

 lines of force through the channel would mean an inverse current 

 in the channel which would just suffice to neutralise the lines 

 added. Thus Ampere's hypothesis really gives no explanation in 

 terms of known facts, but when analysed is a hypothetical device 

 for securing permanent magnets. 



Another hypothesis much more in touch with experimental 

 knowledge has lately gained acceptance. It is founded on the 

 discovery that a moving charge of electricity produces a magnetic 

 field. If, adopting astronomical language, we suppose that a 

 molecule consists of a large positively electrified primary and a small 

 negatively electrified satellite revolving round a centre of mass much 

 nearer the large primary, then it can be shown that the system would 

 be magnetically equivalent to a small magnet with axis through tin- 

 centre of mass perpendicular to the plane of the orbit.* Thus the 

 magnetism of iron and steel would be explained in terms of the 

 magnetism which accompanies moving electricity. Still, that 

 magnetism remains to be explained. 



We shall refer to the molecular hypotheses and to an attempt to 

 determine the strength of the molecular magnets in Chapter XXII. 



* This "electron" hypothesis has been most fully developed by Lar.gevin, 

 Ann. dc Chim. et dc Phys., 8th series [5], 1905, p. 70. A brief account is given at 

 p. 297 infra. 



