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and of causing motion have both equally disappeared. Gravity is the inherent 
liability or disposition of masses to attract other masses. You cannot convert 
electricity or heat into chemical affinity, or any other inherent property of 
matter ; but potential energy may be transferred, — one body having more at 
one time, and another body having more at another time. What now appears 
as heat may appear at other times as electricity, magnetism, or light. All 
these at times are forms of energy, and one must not confound energy with 
force, so as to get into an inextricable labyrinth. 
The Chairman. — Can you give us a definition of those terms ? 
Dr. Haug&ton. — Dr. M‘Cann says, force is that which causes motion, and 
energy is that which does work ; but I think the definition is wrong at 
starting, and, if so, it is quite impossible that the deductions can be 
accurate. If we speak of the force of Nature having its origin in cer- 
tain affinities, then they can only cause motion when the requisite con- 
ditions for motion are present. If there were a stone on this mantel-piece, 
and I were to draw the support away, there would be motion. There was as 
much attraction of gravitation in the earth towards the stone before this was 
done as at the time the support of the mantel-piece was withdrawn ; but the 
mantel-piece kept the stone in its place. The motion, therefore, only takes 
place under certain conditions, so that force is not always that which causes 
motion : it is that which is capable of causing it under certain conditions. 
Then, again, the statement that energy “does work” is equally faulty. 
Energy does not always do work, because, if you have two forces equally 
balanced, — e.g., if you have the two trays of a pair of scales suspended with 
equal weights, you have no motion. But if you lift one of the weights, the 
other immediately begins to move, and the energy which was potential 
becomes actual, the energy being in the weight all the time. Indeed, every- 
thing would be in constant motion throughout the universe if it were not for 
this fact, that the different forces of Nature tend to balance one another. If 
I might venture to depreciate in any degree the tone of the paper we have 
just listened to, and which I admire on the whole, I would say that I do not 
think sufficient appreciation is shown in it for the real progress Science has 
made. I think we have got into a very grand train of thought, which must 
have the effect of leading us on to the most advanced state of progress. The 
origin of the great modern conception we are now here to discuss, was due to 
Count Rumford, about seventy years ago, when he discovered in the boring of 
cannon that heat was a form of motion. I do not know whether he did 
this by way of experiment, but he thought he would utilize what he was 
doing in a scientific point of view, and accordingly adapted vessels of water 
containing thermometers, so that the heat generated by the boring of the 
cannon could be communicated and measured. He carefully arranged his 
machinery in such a way that it was quite evident that the only source of the 
heat was motion — that there was no other source from which the heat could 
be derived but motion. His demonstrations of this fact were unanswerable, 
and he is the true author of the contribution to Science that heat is a mode of 
motion. He proved that the heat was really obtained out of the motion, and 
