ynly 4, 1872] 



NATURE 



iSi 



be distinct realities, viz,. Force and Energy. Further, he states 

 that " the term ' potential ' applied to !• orce or Energy means 

 inictive, but capable of being called into action. Thus, if a 

 weight be raised, a certain amount of energy is expended in 

 raising it, and so long as the body is supported the energy ex- 

 pended in raising it remains potential in it, but when allowed to 

 fall freely //; -racio to the level from which it was raised, the 

 body acquires exactly the amount of energy that was expended 

 in raising it." This too is the view of Tyndall and Balfour 

 Stewart. According to this doctrine, if 1 throw a stone up- 

 wards, say to the height of twenty feet, the energy expended is 

 not lost, but gradually changed in form as the stone ascends. 

 When the stone leaves the hand its energy is actual, at its 

 maximum height it is potential. As a form of potential energy 

 it is a kind ol power existent in the stone, but unexerted until 

 the stone begins to descend. According to the theory of con- 

 servation this unexerted power is not a reality which abides in 

 the stone by virtue of its constitution, but a power that may be 

 lost, and lost as quickly as it was gained. When the slone 

 reaches the ground it possesses no energy beyond a portion of 

 the heat generated by the collision. The advocates of the con- 

 servation hypothesis tell us that the potential energy of the stone 

 at its maximum height is a power to do work: We inquire 

 what woik, and are gravely assured that the stofle has povVer to 

 fall, which it could not do wliea it rested upon the ground ! Let 

 tts suppose that when the stone leaves my hand I was standing 

 on a covered coal-pit two thousand feet deep, and that I remove 

 the cover as the stone descends, if, as Mr. Brooke affirms, the 

 Conservation of Energy is a fact, it follows that when the stone 

 his fallen thi-cugh twenty fee' it will remain suspended over the 

 pit. By its ascent it acquired power to fall only twenty feet, not 

 two thousand and twenty feet. The metaphysicians, so much 

 belaboured by Prof. Tail and other physicists, have ventured to 

 think that the force of gravity has something to do with the fall 

 of the stone. I have certainly found myself unable, even with the 

 aid of the scientific imagination, to form an intelligible idea of the 

 reality supposed to be symbolised by the term " jiotential enei gy. " 

 The theory of thf Conservation of Energy as now maintained by 

 physici.-ts is opposed in several respCctg to the doctrine of the 

 conservation offeree as held by Faraday. Stewart, iJrooke, nnd 

 oihers leach must explicitly that energy is not only constantly 

 changing its form, but always shifting about from one portion of 

 matter to another. If I rhistake iiot, Faraday asserts the very 

 opposite tespefetihg fofce. He seems to teach that eath material 

 particle, into whatever combnations it may enter, retains all its 

 original forces. "A particle of o.xygen,"he says, "is ever a 

 particle of oxygen." 



Mr. Brooke makes other admissions which are as inconsistent 

 with the truth of the doctrine of the conservation as the oi.e I 

 have examined. 1 hese, however, I must leave for the p-e>eut. 

 I feel that the most satisfactory reply to Mr. Brooke's strictures 

 would be to quote here, with two trilling exceptions, the portion 

 of my article wh'ch relates to the conservation of energy. Those 

 exceptions I will novi^ name. First, I withdiaw what I have 

 said respecting Mr. Brooke's view of the nature of latent heat. 

 My sole reason for not in this connection quoting more was that 

 I had assumed his perfect agreement with Prof. Tail. In this 

 it seems I was wrong, since Mr. Brooke declares that he is un- 

 able to derive any definite idea from Prof. Tait's statement. I 

 am sorry that Mr. Brooke should have supposed that the omission 

 of the sentence named w-as due to a lack of literary honesty. I 

 wonder that it did not occur to him that another and more 

 charitable explanation v.-as possible. Secondly, I was in error 

 as to the weights employed by Dr. Joule in one of his experi- 

 ments for determining the mechanical equivalent of heat. But 

 this error relates merely to the form, not to the ultimate result 

 of the experiment ; and consequently in no way invalidates my 

 reasoning. Holding, as I do, that forces are both conserved and 

 correlated, I feel no difficulty whatever in accepting the facts 

 established by Dr. Joule. He avoids speculation regarding the 

 nature of force in itself, and deals exclusively with its manilesta- 

 tions. Thus, his discovery of "the mechanical equivalent of 

 heat" is the discovery of a relation between two classes of effects. 



There is one misrepresentation in Mr. Brooke's review of my 

 article I must here point out. He says, " the reviewer thus 

 quaintly expresses the relations of force, energy, and motion : — 

 A given motion viewed as a cause is force, while the very same 

 motion thought as an effect is energy." But this is not my doc- 

 trine. I am here dealing with the consequences of one of Mr. 

 Justice Grove's assumptions, viz., that if we attempt to analyse 



otlr conception of force, viewed as the cause of any perceived 

 motion, we can get nothing beyond some antecedent motion. 

 Mr. Brooke complains that the misapplication of the term 

 "force " has led to great confusion in physics. His own state- 

 ments are nevertheless unsatisfactoiy, if not contradictory. He 

 accepts the definition of force given by Faraday. But this so- 

 called definition by Faraday is not definition at all. It merely 

 tells us what force does, not what force is. Mr. Brooke adds 

 that the definition " may perhaps vrith advantage be thus ampli- 

 fied ; — Force is a mutual action between the atoms or molecules 

 of m.atter. " 



But these molecular actions or motions are the effects offeree, 

 but not force itself. In no instance whatever can force be re- 

 solved into molecular motion. Mr. Brooke says, "One finds 

 oneself occasionally brought by circumstances into an unwel- 

 come generalisation. Thus the reviewer, speaking of the sup- 

 porters of 'conservation' in the lump, says 'they take it for 

 granted that force is motion and nothing but motion.' This the 

 writer entirely and absolutely denies." Will Mr. Brooke show 

 that this denial is in harmony with his assertion that " force is 

 a mutual action between the atoms or molecules of matter?" I 

 cannot. My reasons for rejecting the assumptions on which the 

 doctrine of the conservation of energy rests are not noticed by 

 Mr. Brooke. These assumptions I have shown belong to false 

 and exploded metaphysics." A false philosophy of causation, it 

 is easy to prove, has greatly retarded the progress of science. 



I perceive that Mr. Brooke has used for reference one of a 

 small number of copies of my article printed for private circula- 

 tion. Unfortunately the paging does not correspond with that of 

 the review. Had I only anticipated the pleasure of an encounter 

 with Mr. B.ooke, I would gladly have sent him the review itself. 

 As ^^r. Bfooke is aware of what passed at a very recent meeting 

 of the Victoria tfistililte, I cannot lorger withhold my name. 



Sale, near Manchester, June 26 John Moore 



Water Analysis 



I.M Nature for June 27, 1872, Mr. Wanklyn directs atten- 

 tion to the facts that his paper on water analysis appeared in 

 1S67, and that in 1S6S he gave some absolute errors obtained 

 with his process. 



Mr. Wanklyn then proceeds to say: — "We have never sair! 

 that distillation of albumin with alkaline permanganate converted 

 the whole of the nitrogen of the albumin into ammonia. The 

 asscrtiim in your article is therefore untrue." Mr. Wanklyn's 

 ideas of triith are probably peculiar, for if he will refer to his 

 paper of June 20, 1867 (Chem. Soc. Jour. vol. v. N.S. p. 4.vS), 

 he will find the following ;-^" Direct experiments in wliich 

 a known quantity of urea, gelatin, and albumin were taken, 

 haveshoA n that all the nitrogen in these substances is obtainable 

 in the form of ammonia when they are subjected to the treatment 

 about to be descril^ed, and has disclosed the very singular fact 

 that boiling with a caustic alkali liberates one-third of the nitro- 

 gen, both of albumin and of gelatin, in the form of ammonia, and 

 that a subsequent boiling with permanganate of potash liberates 

 the other two-thirds." 



Not a word is said in the piaper about carrying on the perman- 

 ganate treatment to dryness, and the only reference to such treat- 

 ment is on page 450, where it is stated that boiling to dryness 

 with potash alone causes the evolution of a "full third " of the 

 nitrogen as ammonia. 



The Writer of the Article 



Scintillation 



C.\N any of your scientific correspondents tell me whether the 

 following observation has been published, and, if so, where ? 



By very slight squinting, or (as suggested to me by a friend) 

 by a slight pressure on one eye, we obtain two images of a star 

 as viewed simultaneously from two stations a few inches apart. 

 We made the experiment some nights ago, and could detect no 

 relation whatever between the scintillations of the two. This 

 seems to explain how little trace of the phenomenon remains 

 when a telescope is used, for in that case we have a sort of inte- 

 gration performed over the whole aperture of the object-glass. 



G. H, 



To Entomologists i^^ITT 



How often is it that the entomologist has to regret the want 



of his net ? The rare butterfly, by some curious perversity, is 



