130 



the motion altogether. Surely, when a thing ceases to move, the motion 

 ceases to exist. What is meant 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 anrient 

 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 



