2-55-4. Peter Guthrie Tait to H. Poincaré

26/3/92

It is clear that I was justified in attributing the gist of M. Poincaré’s first letter to his not having sufficiently read my notice of his book. He has not even yet fully apprehended the bearings of that notice, as a few words will show. Far from being unable to uphold any one of my critical remarks, as M. Poincaré is pleased to hint may be the case, I reassert every one of them, and could easily add to their number.

Let us begin with the particular item of my criticism which M. Poincaré persists in regarding as the most important. My words were: “in his assumed capacity (of pure analyst) he quite naturally looks with indifference, if not with absolute contempt, on the work of the lowly experimenter.” As an illustration of this I instanced M. Poincaré’s ignoration of the thermo-electric researches of Sir William Thomson, Magnus, &c. Then I quoted (in full) two of his remarks on the “Thomson effect”. In the first of these he used the very peculiar phrase

“Sir W. Thomson admet qu’il existe une force &c.”; and in the second he said

“si l’effet Thomson a pu être mis en évidence par l’expérience, on n’a pu jusqu’ici constater l’existence des forces électromotrices qui lui donnent naissance.”

To these he has, in his recent letters, added other like statements. Now, as I understand the matter, Lord Kelvin proved (which, as I take it, means a good deal more than might be implied by “constater”) the existence of the electromotive force which depends on the so-called “Thomson effect” (giving also thereby the means of measuring its amount) by showing that the Peltier electromotive force does not in general fully account for the observed current in a thermo-electric circuit, and may even be directly opposed to it; while no other source of electromotive force can exist save the gradation of temperature in one or both of the metals. He then proceeded, by experiment, to measure the amount of the “Thomson effect” for unit current in various metals, unequally heated. When the passages above quoted from M. Poincaré’s work are compared with the facts just stated, my comments on them will be seen to be fully justified.

It is necessary to add that I made no reference whatever to M. Poincaré’s distinctions between “true” and “apparent” electromotive force: simply because I regard these, along with many other celebrated terms such as “disgregation” &c, as mere empty names employed to conceal our present ignorance.

As to the three chief objections I made to the work of M. Poincaré, every one (author, critic, or onlooker) is entitled to form and express his opinion. I need not restate mine, though I continue to adhere to every word of it: but I may take the following additional remarks on these objections severally.

1. What sort of title to completeness can be claimed for a Treatise, on Thermodynamics, in which no mention is made of the grand principle of Dissipation of Energy; nor of Thermodynamic Motivity, “that possession the waste of which is called Dissipation”?

2. With regard to the measurement of Absolute Temperature, what I did say was that the experiments of Joule and Thomson, which justified them in basing it on Carnot’s Function, were not mentioned by M. Poincaré in this connection. The omission by M. Poincaré of the italicized words makes an absolutely vital change in the meaning of my statement; and enables him to make what, (at first sight only), appears to be an answer to it.

3. As regards the foundation of the Second Law, it is unfortunately clear that M. Poincaré and I must continue to differ: so that further discussion of this point would be unprofitable. For I presume that M. Poincaré has not formed his opinion without careful study of all that Clerk-Maxwell said on the point: so that even a perusal of Lord Kelvin’s latest paper (Fortnightly Review, March 1892) is not likely to induce him to change it.

P. G. T.

PrTL. Tait (1892).

Time-stamp: "23.09.2014 00:36"