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size of the molecules, the latest conclusions are summarised as 
follows, by Sir William Thompson. “ The four lines of argument 
which I have now indicated, lead all to substantially the same 
estimate of the dimensions of molecular structure. Jointly 
they establish, with what we cannot but regard as a very high 
degree of probability, the conclusion that in any ordinary liquid, 
transparent solid, or seemingly opaque solid, the mean distance 
between the centres of contiguous molecules is less than the 
five-millionth, and greater than the thousandth millionth of a 
centimetre. To form some conception of the degree of coarse 
grainedness indicated by this conclusion, imagine a globe of 
water or glass as large as a football (or say a globe of 16 centi- 
metres in diameter), to be magnified up to the size of the earth, 
each constituent molecule being magnified in the same propor- 
tion. The magnified structure would be more coarse grained 
than a heap of small shot, but probably less coarse grained 
than a heap of footballs.” As to the law of intermolecular 
force, we are still in more complete ignorance: again as to the 
nature and origin of molecules, Clerk Maxwell makes a striking 
remark. “It is possible to frame a theory to account for the 
present state of things, by means of generation, variation, and 
discriminative destruction. In the case of the molecules 
however, each individual is permanent ; there is no generation 
or destruction, and no variation, or rather no difference, between 
the individuals of each species. Hence the kind of speculation 
with which we have become so familiar under the name of 
theories of evolution, is quite inapplicable to the case of mole- 
cules. They are as we believe, the only material things which 
still remain in the precise condition in which they first began 
to exist,” when they were created by the Supreme Creator of 
all things visible and invisible. 
2. With regard to the dynamical theory of heat, modern 
physicists are now beginning to regard the great forces of the 
universe, such as heat, and others, as producing effects on bodies, 
of the same kind as are produced by mechanical force. In this 
sense would be a piece of granite when exposed to heat, and 
become distorted and ruptured, its rigidity from the heat rising 
