MOLECULAR HYPOTHESIS 



193 



field. When a magnetising force acts, it is supposed to turn the 

 magnetic molecules round with their axes more or less in the 

 direction of the force, though there is some constraint (not 

 accounted for by Weber) tending to restore them to their original 

 position. But the stronger the magnetising force the more the 

 constraint is overcome, and in a very strongly magnetised bar we 



FIG. 139. 



may suppose that all the molecular axes are turned nearly into 

 line, with their north ends towards one end of the bar, and their 

 south ends towards the other end, forming molecular magnetic 

 chains as in Fig. 140. The poles are to be supposed to be arranged 

 on all the chains as shown on the central chain. The unlike poles 

 of successive members of a chain are close together so as to neutralise 

 each other, but obviously each chain will have an unneutralised 



TV J Tl 3 TV .? TV 



7V STVSTV3TLSTV 



FIG. 140. 



pole at each of its ends so that there will be a number of un- 

 neutralised NSP's on the surface near one end of the bar, and an 

 equal number of unneutralised SSP's near the other end. And 

 the molecules all having equal poles, the total polarity is the same 

 at the two ends. Further, if the bar be cut through at A B, on 

 the new surface to the left a row of unneutralised SSP's will be 

 < \posed, while on the new surface to the right a row of NSP's will 

 be exposed. Obviously, as we do not cut through the molecules 

 we cannot obtain polarity of one kind alone. 



On this hypothesis there is a limit to the magnetisation which 

 ;\ given bar will undergo, reached when all the molecular magnets 



