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vocabulary of science as nothing less than a calamity. What is the reality 
symbolized by these words, and where is it to be found ? A simple illustra- 
tion will serve both to indicate my objection to the use of the term potential 
energy, and also to bring out my own view. Here are two stones, each of 
them at the surface of the earth, weighing one pound. One of them I place 
close to the edge of the mouth of a coal-pit, one hundred yards deep ; the 
other I throw upwards, which, at its maximum height of one hundred feet, 
is caught on the ledge of a rock. Now the theory of the conservation of 
energy requires us to believe that the latter stone has, by rising, acquired a 
potential energy — a power of doing work of which the one remaining on the 
ground is altogether destitute. The stone resting on the rock can fall, while 
— so says the theory — the stone on the edge of the pit cannot. Mr. Brooke 
has referred to Dr. Joule’s experiments. I will only say that in none of these 
as explained to me by Dr. Joule himself, can I find anything opposed to the 
positions I have been maintaining. The beautiful experiments by which he 
determined the mechanical equivalent of heat, I am prepared to show, lend 
no support whatever to the doctrine that the various forms of energy are ' 
mutually convertible. In conclusion, I would, sir, thank Mr. Brooke for his 
able criticism of my opinions as given in the paper this evening, and 
elsewhere. Every intelligent and sincere objector I ever regard as a true 
friend, both to myself and the great cause of truth. 
Bev. W. J. Irons, D.D. — I think the paper which has been read, and the 
observations which have since been made upon it, are so important that 
they need careful and minute consideration ; and a hasty discussion on a 
subject of so much depth and importance would scarcely be becoming in a 
scientific Society like this. For my own part, I feel strongly disposed to 
acquiesce in the distinction which was drawn by the last speaker— namely, 
that there is indeed a conservation of power, but not a conservation of 
energy. I think that the conservation of power he refers to is almost iden- 
tical with the doctrine of Albert and Thomas Aquinas concerning the impos- 
sibility of either augmenting or diminishing the sum-total of the physical 
universe — the impossibility, for instance, of annihilation, affirmed by Albert 
the Great in very distinct terms. I made up my mind some years ago, when 
I first considered the doctrine of the “ conservation of forces,” that it meant 
no more than had been understood under other terms in the middle ages ; 
but probably at the present moment we are unable to decide what some gentle- 
men ultimately mean when they lay down the law so positively about this 
“ conservation of forces.” Is there no initiation of motion ? If Mr. Stuart 
Mill were here to-night, he might perhaps be able to tell us whether he 
allows any such thing as a kind of initiation of action which is not a 
deduction from previous forces in the universe. That would at once raise 
the question whether materialism be the sum-total of the universe. I 
should hojDe he would hardly go that length. Scepticism itself would assist 
him there, as it would scarcely propound what would be almost a negation 
of mental action itself. The whole subject is one which we are right 
in considering with gravity. The philosophy of the subject lias yet to 
