THE MOLECULAR PROCESS IN MAGNETIC INDUCTION. 263 



the area of the looj) in our diagrams. This energy is dissipated; that 

 is to say, it is scattered and rendered nseh'ss; it takes the form of heat. 

 The iron core of a transformer, for instance, which is having its mag- 

 netism reversed with every pulsation of the alternating current, tends 

 to become hot for this very reason; indeed, the loss of energy which 

 happens in it, in consecpience of magnetic hi/sfcresLs, is a serious draw- 

 back to the efticiency of alternating-current systems of distributing 

 electricity. It is the chief reason why they require much more coal to 

 be burnt, for every unit of electricity sold, than direct-current systems 

 require. 



The molecular theory shows how this waste of energy occurs. When 

 the molecule becomes unstable and tumbles violently over, it oscillates 

 and sets its neighbors oscillating, until the oscillations are damped 

 out by the eddy currents of electricity which they generate in the sur- 

 rounding conducting mass. The useful work that can be got from the 

 molecule as it falls ov^er islessthan the work that is done in replacing it 

 during the return portion of the cycle. This is a simple mechanical 

 deduction from the fact that the movement has unstable phases. 



I can not attemjtt, in a single lecture, to do more than glance at 

 several places where the molecular theory seems to throw a flood of 

 light on obscure and complicated facts, as soon as we recognize that 

 the constraint of the molecules is due to their mutual action as mag- 

 nets. 



It has been known since the time of Gilbert that vibration greatly 

 facilitates the process of magnectic induction. Let a piece of iron be 

 briskly tapped while it lies in the magnetic held, and it is found to take 

 up a large addition to its induced magnetism. Indeed, if we examine 

 the successive stages of the x>rocess while the iron is kept vibrating by 

 being tapped, we find that the first stage {a) has practically disaji- 

 peared, and there is a steady and rapid growth of magnetism almost 

 from the very first. This is intelligible enough. Vibration sets the 

 molecular magnets oscillating, and allows them to break 1 heir primi- 

 tive mutnal ties and to res])ond to weak defiecting forces. For asimi- 

 lar reason, vibration should tend to reduce the residue of magnetism 

 which is left when the magnetizing force is removed, and this, too, 

 agrees with the results of observation. 



Perha])s tlie most effective way to sliow tlie iiiHuencc of vil)ration is 

 to apply a weak magnetizing force first, before tap])ing. If the force 

 is adjusted so that it nearly but notciuite 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 i)iec(' is tapped they go over like 

 a house of cards, and magnetism is accpiiied with a rush. Tajjping 

 always has some elfect ol'the same kind, ev^Mi though there has been 

 no si)ecial adjustment of the Held. 



And other things besides vii)ration will act in r. similar way, ])recii)i- 

 tating the break-ui) of mole(;ular groups when tlie ties are already 



