Manchester Memoirs, Vol. li. (1907), No. 15. 15- 



forces with them. The dissenters give one another mutual 

 support. We can suppose their little community enlarged 



++ 



A- 



A 



\K 



-it 



■> <- 



<r 



A- 



As 



A- 



- <e 



Fig. 5- 



as much as we please, but it still remains different from 

 the rest of the crystal. 



The matter will become clearer if we study experi- 

 mentally a model in which polar molecules are pivotted 

 on centres on a glass plate, so that their shadows may 

 be thrown on the screen, and you can watch how they 

 behave under the action of their mutual forces. 



Begin crystal building with two molecules, and notice 

 how they accommodate themselves to one another first of 

 all. This, if you like, is the settlement from the liquid 

 state. You see there is a little hesitation at first. Four 

 of them have now taken up the same position as the four 

 shown in the drawing {Text-fig. 3.) That is the position 

 of most stability, and if we were dealing with a small com- 

 munity they would necessarily take up this position. If 

 I displace them from it you will see that they return to it. 

 Now we will take a group sufficiently large to have a 

 dissenting community set up in it. You see that at first 

 the whole group is in proper tactical formation corre- 

 sponding to complete stability — the formation namely of 



