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the motion altogether. Surely, when a thing ceases to move, the motion 
ceases to exist. What is me&nt by such expressions as latent or stored-up 
motion is a force or power which, after a certain thing has ceased to move, is 
capable of setting it in motion again ; but if we use terms after this fashion, 
how is it possible to reason accurately ? So I apprehend the term potential 
motion, if translated into simple English, must mean that a certain thing 
which is not in motion is capable of being set in motion. No doubt the sub- 
ject of motion may be made to involve many most serious metaphysical diffi- 
culties — shall I say puzzles— as the most ordinary acquaintance with am ‘tent 
philosophy proves. It is perhaps better to give up all attempts to define the 
subject metaphysically, and to be content to use the term as it daily appears 
as a phenomenon before our eyes. But it is far from uncommon to speak of 
certain mental states as though they were motions likewise. To do so may 
be well enough for popular purposes ; but if we are dealing with subjects scien- 
tifically, the only result is to make our confusion worse confounded. I would 
submit that the states in question cannot with any propriety be denominated 
motions, except metaphorically. What common idea is there when I say, 
I have been deeply moved by a tragical story, or I have been carried 
on at the rate of fifty miles an hour in a railway carriage ? I own that 
I am also often sadly puzzled by the use of the term “ energy.” It seems to 
me difficult to assign any definite meaning to it, unless we mean by it the 
active state of a thing, as different from its passive state — a thing doing 
something, as distinct from a thing doing nothing — action as contra- 
distinguished from passion. But I think that I have both heard and read of 
“energy,” which is not “energy” in any of these senses. Now, “energy” which 
has ceased from an active state, and passed into an inactive one, seems to me to 
be “ energy ” no longer, but to have become something else. I am, therefore, 
quite unable to understand what such a term as “ potential energy ” means, 
except that it is one specially invented for the purpose of producing confusion 
of thought. What I presume is really intended is, some power which can 
set a thing acting again after it has ceased to act. But if this is the real 
meaning, why not express it in perspicuous language ? One portion of the 
paper to-night — perhaps its most important portion — has not been touched 
upon in the discussion, as to whether it is, or it is not, possible to convert 
material forces into mental states ; or, in one word, whether so much 
material force can correlate into so much mental power. I think it 
unquestionable that a number of the most absurd propositions have been 
uttered on this subject. It is broadly stated by a number of writers at the 
present day that all the phenomena of mind are merely different forms of 
so much material force. The multitude of absurd statements uttered on 
this point, if not very serious, would be very amusing. Just fancy what our 
friends would call the force of so much self-sacrifice correlated into so much 
electricity ! I believe that sound is often spoken of as a mode of motion. Its 
material vehicle unquestionably is, but sound itself consists of two factors, a 
material apparatus and a perceptive power of the mind, and if either of them 
is wanting, what we call sound cannot exist. There is a good deal on the 
