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formation the cleavage is octahedral, for such cleavage over- 
comes the attraction of each molecule to three others, while 
any other would have to overcome the attraction of at least 
four. And in the dodecahedral the cleavage is in like manner 
parallel to the faces, as this cleavage destroys the cohesion of 
two poles, while the two other possible cleavages would destroy 
the cohesion of three and four respectively. 
«‘ With respect to the cause of decrements, they will evi- 
‘dently result from the loss of polarity in the external mole- 
cules, and this loss is what we would have every reason to an- 
ticipate ; for if we consider the attraction of the particles to 
arise from the attraction of a fluid contained in them, and that 
this fluid is only held in its place by a certain coercive power 
of the molecule itself, as is the case with a magnet, it will fol- 
low, that as the crystal increases in size the combined attrac- 
tion of the whole fluid will draw from the extreme molecules 
such fluid as they may contain, and thus they will lose their 
polarity. 
«* Thus, if the time which elapses while a layer of molecules 
is being laid on a cube, is equal to that which elapses while 
the polarities of the corner molecules is being removed, octa- 
hedral faces will appear; and in a similar manner we can ex- 
plain all the other cases. 
‘‘ Tn this theory we must of course suppose the particles of 
the fluid to be infinitely smaller than those of the crystal.” 
