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matter of that compound, but by the amount of energy asso- 
ciated with that collocation of matter. She has been able to 
point out many instances of compounds composed of the same 
matter, but possessed of different amounts of energy, and, at 
the same time, of very different properties. And moreover, 
chemistry aided by physics, has concluded that the properties 
of a body 4 are dependent on the variations of the energy of the 
body, and not on its total value/ and therefore that 4 it is un- 
necessary, even if it were possible, to form any estimate of the 
energy of the body in its standard state/ (I quote from that 
remarkable little book of the late Professor Glerk Maxwell, 
Matter and Motion.) 
Whenever science made the advance from the vague con- 
ception of 4 principles ’ and 4 imponderable matter ’ to the 
definite conception of 4 mass/ 4 motion/ and 4 energy/ she was 
able to recognize the truth which lurked under the cumbersome 
and inexact nomenclature of the Pblogistean chemists. 
I have said that, as usual, the dispute between the Phlogis- 
teans and their opponents was proved to be a question of 
meaning of words : as usual, also, subsequent research showed 
that while both were wrong, both also were right. 
Composition is important, but composition is not all. The 
burnt body has properties differing from those of the unburnt 
body, because it has lost a certain amount of 4 the power of 
doing work / but it has a less power of doing work because it 
is possessed of a structure different from that which it possessed 
before. Composition and properties, energy and structure, are 
closely connected : to determine the exact relations existing 
between these, under stated conditions, is still the fundamental 
problem of chemical science. 
We can define Energy: the Phlogisteans could not define 
Phlogiston. But in the ethereal philosophy of the future will it 
not be said of the present workers in science that they could 
not define Ether, but even spoke of it at times as 4 not gross nor 
ponderable matter ? 1 
The theory of Phlogiston was continued and developed in 
the theory of Caloric : the theory of Caloric is vastly extended, 
simplified, and rendered definite in the theory of Energy : and 
the theory of Energy seems destined to be largely extended by 
the Ethereal theory now in its infancy. 
Mankind has until lately been content with space of three 
dimensions, but the bolder and more dashing spirits among the 
mathematicians have dared to look forward to a better world 
than this where they may revel in space of four dimensions. 
What a strange world must that be ! what a fearful place for 
a mathematical examination, when we remember that the 
inhabitants thereof — if there be inhabitants — may turn 
