46 FORMATION OF SHELLS OF ANIMALS, ETC., 
which they are all placed are alike, the electricity of every 
one will doubtless be the same, and hence they will repel 
one another. The second case is a mere instance of 
thermo-electricity, in which electrical excitation is produced 
by the unequal conduction of heat. Hence there is no 
extravagancy in the inference that in both these cases the 
crystallizing particles, being under the infiuence of like 
electricities, should be self repulsive, or rather, as this 
state is acquired in an instant, and as instantaneously 
brought imto operation, self-propulsive. Indeed, the 
bare fact of these particles becoming rectilinearly disposed 
under such circumstances is an experimental proof of the 
existence of an agency capable of exciting upon them a 
repulsive power. And as there is no other known power 
capable of producing, under the same circumstances, a like 
effect, excepting electricity, it may fairly be considered as 
the power in question. As to the adequacy of simple 
electricity to account for this fact and the ordinary 
phenomena of crystallization, it may be observed that the 
impulsive power of large discharges of this agent are too 
well known to leave any doubt upon this head. It is 
certain that, in the last experiment, the sudden production 
of perfectly crystalline forms in such hard globular bodies 
must have required a considerable amount of mechanical 
force, considering that the molecules of these bodies could 
not have taken up a new position without in some degree 
displacing the particles contiguous to them, and so dis- 
turbing, more or less, the cohesions of the entire calculus. 
But what other known force is there m nature which could 
have achieved this besides electricity? Caloric, actmg m 
different ways and through different means, might have 
broken these bodies into pieces, but it could not have put 
them together again in regular geometrical forms. To 
4 
