1891.] on the Molecular Process in Magnetic Induction. 



397 



Fig. 13. 



cally disappeared, and tliere is a steady and rapid growth of mag- 

 netism almost from the very first. This is intelligible enough. 

 Vibration sets the molecular magnets oscillating, and allows them to 

 break their primitive mutual ties and to respond to weak deflecting 

 forces. For a similar reason vibration should tend to reduce the 

 residue of magnetism which is left when the magnetising force is 

 removed, and this, too, agrees with the results of observation. 



Perhaps the most eflfective way to show the influence of vibration 

 is to apply a weak magnetising force first, before tapping. If the 

 force is adjusted so that it nearly but not quite reaches the limit of 

 stage (a), a great number of the molecular magnets are, so to speak, 

 hovering on the verge of instability, and when the piece is tapped 

 they go over like a house of cards, and 

 magnetism is acquired with a rush. 

 Tapping always has some effect of the 

 same kind, even though there has been 

 no special adjustment of the field. 



And other things besides vibration 

 will act in a similar way, precipitating 

 the break-up of molecular groups when 

 the ties are already strained. Change 

 of temperature will sometimes do it, or 

 the application or change of mechanical 

 strain. Suppose, for instance, that we 

 apply pull to an iron wire while it hangs 

 in a weak magnetic field, by making it 

 carry a weight. The first time that we 

 put on the weight, the magnetism of the 

 wire at once increases, often very greatly, 

 in consequence of the action I have just 

 described (Fig. 13). The molecules 

 have been on the verge of turning, and 

 the slight strain caused by the weight 

 is enough to make them go. Remove 

 the weight, and there is only a com- 

 paratively small change in the magnet- 

 ism, for the greater part of the molecular 

 turning that was done when the weight 

 was put on is not undone when it is 

 taken ofi^. Reapply the weight, and you 

 find again but little change, though there 

 are still traces of the kind of action which 

 the first application brought about. That 



is to say, there are some groups of molecules which, though they were 

 not broken up in the first application of the weight, yield now, because 

 they have lost the support they then obtained from neigh l)ours that 

 have now entered into new combinations. Indeed, this kind of action 

 may often be traced, always diminishing in amount, during several 



Effects of loading, unloading, and 



reloading a soft iron wire in a 



weak magnetic field. 



