Oct. 25, 1877] 



NATURE 



547 



Prof. Hoffmann, of Berlin, whether that doctrine any longer 

 finds support among scieniific men in Germany. //« rcplv was a 

 most emphatic mgalive ; the doctrine, he said, heing one which no 

 man of science with whom he is acquainted would think worthy 

 of the slightest attention. Yet in Mr. Wallace's judgment (query 

 in Mr. Crookes's also ?) the unanimous verdict of the scientific 

 world of Germany, to say nothing of England, is a prejudiced 

 one ; only Mr. W. and his spiritualistic allies appreciating cor- 

 rectly the real force of the evidence originally advanced by 

 Reichenbach, and confirmed by those trustwoithy (?) authorities, 

 Drs. Ashbumer and Gregory. 



In thus setting his own judgment on a question which lies 

 altogether outside the scientific domain which he has made his 

 o.in, at;ainst the unanimous verdict of the eminent physicists 

 and physiologists who have carefully " tried " the Od-force and 

 " found it want ng," and in rebuking myself and those who think 

 with me for our incredulity, does not Mr. Wall.ice put himself 

 somewhat in the attitude of his old opponent, John Hampden, 

 who thinks everybody either a fool or a knave who maintains the 

 earth to be round? William B. Carpenter 



October 22 



Potential Energy 



With reference" to the views of "John O'Toole" on the 

 subject of energy perhaps you will allow me to say how one of 

 the class to whicli "poor Publius " belongs has conceived the 

 matter ol terminology with satisfaction to himself. 



1. Energy being unanimously defined by " the doctors " to be 

 "capacity for doing work," and also energy conveying in its 

 derivation the notiun of activity, this term is properly applicable 

 only to the bodies of material systems the motions of which are 

 contemplated. Hence all energy is in its nature kinetic — the 

 very term kinetic is logically included in the term energy. 



2. When a material system is in motion it actually possesses, 

 ipso facto, a capability of doing work, that is to say, it has 

 actual energy. 



3. When in any configuration of the system we contemplate as 

 possible the action of causes which will alter its motions and give 

 it a second configuration, the excess of the energy which it would 

 possess in this second configuration over the energy which it 

 possesses in the first is properly called its potential energy in the 

 first configuration. 



4. The asseition that in any configuration the sum of the 

 energies, actual and potential, of a material system is constant, is 

 what Kant would call an analytical proposition, or what "X." 

 (quoting Herschel) calls "only a truism after all." But I further 

 remark — 



5. That this truism is not the prmciple of the conservation of 

 energy, but that this principle is a true " synthetical proposition " 

 which some fairly regard as an almost immediate deduction from 

 Xev.ton's third law, and which others regard as proved by often 

 repeated and much varied experiment; and hence that "X.'s" 

 statement of this great principle in the form — "The sum of the 

 actual and potential energies of tkeniiwerseis a constant quantity," 

 (the italics are nine) is not its proper definition. 



6. That, leaving the consideration of bodies, and referring to 

 forces, the term to be employed instead of energy is work, and 

 that the term analogous to the "potential energy of bodies" is 

 the "potential work of forces," this latter being the amount of 

 work which they are capable of doing in displacing their points 

 of application from their actual configuration to any fixed chosen 

 one. 



7. That by the expenditure of a fixed amount of work on any 

 material system the same amount of actual energy (whose type 

 is \ m v'-) is under all circumstances produced, and that, through 

 whatever forms this actual energy is made to pass, if the whole 

 of it is always utibsed, it will finally be reconvertible into the 

 same original amount of work, this being the principle of the 

 conservation of energy. 



8. That instead of the statement in 5, we must substitute the 

 synthetical proposition that " the sum of the actual energy of the 

 bodies in the universe and the potential wok of its internal 

 forces is a constant quantity," and the same is true of every 

 material system which is regarded as complete in itself ; or in 

 other words, wherever and however a given quantity of potential 

 work is lost by the forces of the system, this always appears in 

 the shape of a fixed quantity of actual energy, in the form which 

 we call heat, or in some Crther. 



Hence we have energy, actual and potential, of bodies ; and 

 work, actual and potential, of forces. 



A few remarks in conclusion. "J. M." has very happily 

 illustrated the propriety of the expression potential energy, as, 

 in strict consequence of the definition of energy, a potential 

 capacity of doing work ; and if in his illustration the "power of 

 purchasing" is considered with reference to a further object, 

 there may be not merely a "double remotion from " what we 

 may regard as "tangibility," but a remoiion of a higher muUiple 

 order. " W. G." has well explained that it is only in conse- 

 quence of the fixedness of the earth that the potential energy of 

 the system of the earth and stone is by the " doctors " located 

 in tlie stone. Finally, I can hardly conceive how " X. ," who has 

 devoted so much attention to the literature of this subject, can 

 have fallen into such a grievous error with regard to the clock. 



Royal Indian Engineering College, G. M. Minchin 



Cooper's Hill 



Your " Potcnti.il Energy " corespondents will find three 

 letters on the " Conservaiion of Energy" in the Engineer for, 

 January 12 and 19 and Febru.ary 2 which may interest them. 

 Tlie writer " *n " assum.es that all the phenomena of force are 

 explained by the theory that only matter and motion exist, and 

 that what we ciU potential "energy" is only "quantity and 

 motion," which motion is indestructible but difTusible. Z. 



London, October 20 



Origin of Contagious Diseases 



I HAVE been much struck by the following passage in Dr. 

 Richardson's address, Nature (vol. xvi. p. 4S1) : — 



" (<-) That as regards the organic poisons themselves and their 

 physical properties, tlie great type of them all is represented by 

 tlie poison of any venomous snake. . . . It is the type of all 

 the poisons which produce disease." 



Now has it been really proved, by experiment, that the poison 

 of snakes produces the effects characterising the contagia ? viz., 



"(0) . . . Each particle of any of these poisons brought into 

 contact either with the blcod of the living animal or with certain 

 secretions of the living animal, possesses the property of turning 

 the albuminous part of that same blood or that same secretion 

 into substance like itself. ..." 



In other words, if an animal is suffering from snake poison 

 does its blood or any of its secretions acquire the power of 

 transmitting the disease, i.e., the effects of a snake's bite, to 

 another individual, as is the case with an animal affected with 

 carbuncle, ghnders, hydrophobia, &c. , &c. ? 



Unless this question has been decided in the affirmative it 

 would appear rather difficult to uphold the sentence (<r) as quoted 

 above. D. W, 



Freiburg in Brisgau, G. J., October 14 



[Dr. Richardson informs us that D. W. does not properly 

 understand his argument. Dr. Richardson does? not suppose 

 that the person or animal poisoned from a poisonous snake is, 

 in turn, poisonous, although that may be the fact. He merely 

 uses the illustration that as a poisonous snake secretes a poison 

 so an infectious person is for the time secreting a poison.] 



I SEE by your issue of October 4, that Dr. Richardson has 

 honoured me by mentioning my name and placing me as the 

 first, in modern times, to advocate the hypothesis that hving 

 germs are the exciting agents of epidemic and infectious diseases. 

 But he says further, " I protest, I say, that this hypothesis is the 

 wildest, the most innocent, the most distant from the phenomena 

 it attempts to explain, that ever entered the mind of man to 

 conceive." It may be so, but I look in vain through the whole 

 story he narrates in his lecture to find a rational substitute for it, 

 and it appears to me desirable at the present juncture that the 

 principles of the germ theory, as I have interpreted them, should 

 stand side by side with Dr. Richardson's " glandular theory." 

 It is now nearly thirty years since I endeavoured to find some 

 common root or cause for those diseases which we find in plants, 

 animals, and man, and which are communicable among the 

 individuals of each order in nature ; also, in some instances, from 

 one order to another. During that thirty years every step in 

 scientific research and medical experience as far as my inquiries 

 have carrried me, has tended to confirm the views I put forward 

 in my original "Essay" and in subsequent papers read before 

 the Epidemiological Society. Notably the latest advocates of a 

 germ theory are tivo of our most eminent men, the one a leader 

 in science, the other a leading physician. I need hardly say I 

 allude to Prof. Tyndall and Sir Thomas Watson; surely these 



