PREFACE TO SECOND EDITION.

IN preparing a Second Edition for the press, I have adhered to my original plan of publishing these Lectures just as they were taken down by the shorthand writers. I have, however, altered here and there a mere word or two, and in a few places, where it appeared to be called for, I have added an explanatory sentence.

Herr Wertheim, who is engaged in translating the work into German, has kindly called my attention to an article in the second edition of Clausius' Mechanische Wärmetheorie which has reference to a discussion raised by that author in Pogg. Ann. (1872.) Three letters were written by Clausius and three by myself—all of which appeared in the Phil. Mag. (see foot-note to p. 118.) The first alone of my letters was sent to Professor Poggendorff, as I did not wish to occupy more than was absolutely necessary of his space with what I could not help anticipating would be a perfectly fruitless controversy.

I disclaimed at once and utterly the imputation of irritation made by Clausius. I simply said, in answer

to his charges of deliberate suppression, etc., 'Such language may amaze and amuse, it is too reckless to produce irritation.' And in my last letter in the Phil. Mag. (September 1872) I described my position as follows:

Professor Clausius has so long, and so repeatedly, claimed as his own the correct proof of the Second Law of Thermodynamics, that no one can be astonished to find him unwilling to allow that his claims are unfounded.

But I must protest against his making accusations of deliberate suppression, etc., and repeating them in the indirect and offensive form of a statement that he did not apply them to Sir W. Thomson.

There has been nothing in the language I have employed, even had it been tenfold more pointed, which is not admissible in fair and temperate discussion. I have made no charges (though strongly tempted to do so by Professor Clausius' first letter), I have simply examined historical facts and given what appears to me to be the natural and inevitable conclusion from them. But, after having taken every precaution to insure accuracy, to be first accused of deliberate suppression, and then to be told that the tone of my far too mild reply renders it impossible for Professor Clausius to continue the discussion, is a trifle too much.

In common with all the scientific friends I have consulted, I am unable to perceive that Professor Clausius has ‘refuted' any one of my former remarks, or that he is likely to be able to refute any of the others though he says it can be easily done. Let Professor Clausius attempt the refutation, if he thinks proper to do so : but in future it is to be hoped he will leave offensive and unjust charges unmade. As I consider that my last letter contains all that it is necessary for the present to say for my own view of the matter, I shall continue to maintain and to promulgate the opinions therein expressed, until convinced by argument, not by personalities, that they are incorrect or insufficient.

Professor Clausius now says that I have shirked the two main charges brought against me. I am not of

that opinion, but I shall endeavour to make up for any possible defect of that kind. I cannot now go fully into the whole matter, but as some parts of the charges are, if well founded, applicable to this work, I shall allude to them here.

Clausius' first charge is that there can be no doubt that my Sketch of Thermodynamics1 owed its origin principally to my purpose of claiming the Mechanical Theory of Heat as far as possible for the English (British) nation,' and he adds that he 'can bring forward the most definite grounds for this opinion.' I am, indeed, curious to know what these grounds can be, seeing that the deduction to which they have led my assailant is so entirely at variance with my own recollections. So far as I am aware, my book owed its origin to the desire expressed to the Editor of the North British Review, by various scientific or practical men, mainly engineers, that two articles of mine which had appeared in that work should be reprinted, for convenience of reference. As I found that I should thus, by adding a short chapter, make a useful manual for students, I agreed at once to the proposal. There can be no question here as to a view of claiming anything for the British nation.

But perhaps Professor Clausius means that the Review 1 Edinburgh, Edmonston and Douglas, 1868.

articles were originally written with this view. Here again my memory can recall nothing beyond a request by the Editor that I should review certain works on the Modern Theory of Energy, and specially on the branch of it which relates more particularly to Heat. I found that it was impossible to write articles which should be intelligible to the mass of the readers of the Review unless I were to give them in the main the form of a sketch, partly historical, of the whole subject.

I am not conscious of having anywhere stretched a point to claim for Joule or Thomson what I did not believe to be entirely theirs. On the contrary, I now see that I unwisely, though I thought at the time justly, added in favour of Clausius some paragraphs to an abstract of his work, which, at my request, had been kindly drawn up for me by my friend the late Professor Rankine. I made this request to Rankine because Clausius had, in a private letter to me, protested against some statements in my first Review article. Rankine's acquaintance with the details of Clausius' work was, I knew, at that time much more complete than mine.

This point, however, I shall discuss more fully in a second edition of my Sketch, shortly to be published.

As to the general question of writing too much in British interest, I will content myself with quoting