;68 



NATURE 



[October 15, 189] 



complete removal of the force brings them into the con- 

 dition with which we began (Fig. 3). 



If we were to picture a piece of iron as formed of a 

 vast number of such pairs of molecular magnets, each 

 pair far enough from its neighbours to be practically out 

 of reach of their magnetic influence, we might deduce 

 many of the observed magnetic properties, but not all. 



Fig. s- 



In particular, we should not be able to account for so 

 much residual magnetism as is actually found. To get 

 that, the molecules must make new connections when the 

 old ones are broken ; their relations are of a kind more 

 complex than the quasi-matrimonial one which the ex- 

 periment exhibits. Each molecule is a member of a larger 



community, and has probably many neighbours close 

 enough to affect its conduct. v" 



We get a better idea of what happens by considenng 

 four magnets (Fig. 6). At first, in the absence of deflect- 

 ing magnetic force, they group themselves in stable pairs 

 — in one of a number of possible combinations. Then — 



as in the former case— when magnetic force is applied, 

 they are at first slightly deflected, in a manner that exactly 

 tallies with what I have called the stage a of the magnet- 

 izing process. Next comes instability. The original ties 

 break up, and the magnets swing violently round ; but 

 finding a new possibility of combining (Fig. 7), they take 

 NO. I 146, VOL. 44] 



to that. Finally, as the field is further strengthened, they 

 are drawn into perfect alignment with the applied mag- 

 netic force (Fig. 8). 



We see the same three stages in a multiform group 

 (Figs. 9, 10, II). At first, the group, if it is shuffled by 

 any casual disturbance, arranges itself at random in lines 

 that give no resultant polarity (Fig. 9). A weak force pro- 

 duces no more than slight quasi-elastic deflections ; a 

 stronger force breaks up the old lines, and forms new ones 



more favourably inclined to the direction of the force 

 (Fig. 10). A very strong force brings about saturation 

 (Fig. II). 



In an actual piece of iron there are multitudes of groups 

 lying differently directed to begin with — perhaps also 

 different as regards the spacing of their members. Some 

 enter the second stage while others are still in the first, 

 and so on. Hence, the curve of magnetization does not 



Fig. 9. 



consist of perfectly sharp steps, but has the rounded out- 

 lines of Fig. I, 



Notice, again, how the behaviour of these assemblages 

 of elementary magnets agrees with what I have said 

 about residual magnetism. If we stop strengthening the 

 field before the first stage is passed — before any of the 

 magnets have become unstable and have tumbled round 

 into new pla^-es — the small deflection simply disappears, 



