14 



Ewinq, The Structure of Metals. 



pole in one brickbat attracts an opposite pole in another, 

 and that two like poles will repel, and two unlike poles 

 will attract. Suppose now the crystal to be built by a 

 gradual assemblage of such polar molecules. Begin with 

 one, and put down others, one by one, in the position 



<K-^ 



A 



<A- + 



Fi s . 4. 



of greatest stability with respect to it. By the time you 

 have put down four molecules, they have taken the 

 positions shown in Text-fig. 3. And similarly Text-fig. 4 

 shows the arrangement that is found in a much more 

 numerous group, when the condition of maximum stability 

 is satisfied in the process of crystal building. 



I want next to show you the establishment of what I 

 shall call a little group of dissenters. I use that descrip- 

 tion merely as a short term to express a group, the 

 members of which keep each other in countenance, but 

 are out of complete harmony with their environment. We 

 can establish such a group by supposing two of these 

 molecules turned round. They are still stable, but not so 

 stable, and not so comfortable, as they were to begin 

 with. Text-fig. 5 shows such a dissenting group at a, b, c. 

 Their position may be strengthened by turning one or 

 more other molecules, such as d, round, so as to join 



