98 From Matter to Man. 



This has, in effect, been already done, for by demon- 

 strating how all atoms as magnets attract each other 

 by the laws of like-material-attraction, sexual-material- 

 selection, and polarity, we virtually prove that cohesion 

 is caused by these primary forces. 



Cohesion also includes the problems of crystallisa- 

 tion and cleavage. Tyndall practically solved these 

 problems by repeating Grove's experiment of passing 

 an electric current through a glass cylinder containing 

 fine magnetic mud (oxide of iron) suspended in 

 water. Previously to the introduction of the current 

 the water was turbid and the particles promiscuously 

 strewn in the liquid; but the moment the current 

 passed, all set their lengths parallel to a common 

 direction. (In effect, magnetic induction ensued.) 

 By the manner, therefore, in which the atoms and 

 molecules of all substances in suitable condition (all 

 being magnets) combine by polar law, whether in 

 regular sequence or promiscuously, we now perceive 

 how all varieties of cohesion could be effected, all 

 kinds of crystals built up, and all manner of cleavages 

 produced. Tied, however, to the present law of 

 gravitation, Tyndall was reluctantly compelled to 

 relinquish polarity as a cause of cohesion, and to 

 advocate — for slaty cleavage, if not for all — a theory 

 of pressure. For further details of cohesion, see 

 " Mineral Evolution." 



