the good points of this intimacy, which indeed is a novel one.
The scientific man of today has a large and attentive audience; and, except he be a devotee to the more abstract of the sciences, he is sure of immediate praise. This, too, is a good result from the close connection. But the effect has been, partly, to make the scientist speak in a manner almost too elementary; in endeavoring to make all things plain, he has been obliged to hide the very highest of his researches, because their demonstration has required too great a stretch of intellect from his hearers.
This has been, partly, inseparate from the form of instruction by lectures, in which form it is, of course, impossible to obtain much close attention to the more complex of his truths, which only allow themselves to be stated in mathematical symbols. We may assume the public of a scientist like Tyndall or Huxley to be composed of three classes: 1. Of scientists themselves, who can and must consult their original memoirs, and who have besides the power to supply any lacunae in reasoning; 2. Of the general public; and, 3. Of a large and important class of young men, students, to whom science is a cultivator, and who desire didactic treatises which shall give concisely and rigorously the essence of a subject, and which shall not require them to consult publications of scientific societies, which works are often beyond their reach, and to which, at any rate, but few would go.
It is, therefore, with real gratitude that we must look to Prof. Maxwell for his essay on the Theory of Heat.
It fills, exactly, a place before vacant. By it we are led in a logical order, which is very beautiful, from the simple idea of temperature, through the registration of this temperature, and finally to the complex idea of the measure of heat. From this point an analysis of the book would be almost a history of the development of the science. The subjects of isothermals and adiabatics are fully treated, and the elementary principles of heat engines are stated and proved.
While all this is done, so that a young student, with due attention, may follow the argument, we warn him that the book is no child's play. There are no useless words spent on explanations, but enough is left to keep his mind clear and busy. And it is here, too, that we may speak of the admirable manner of the book which is rigorous throughout. It is an excellent preparation, too, to the memoirs of Clausius, whose mathematical essays are the acknowledged classics on the subject of heat, and who still leads us in the most startling way and at once to differential equations, as if they were our daily bread.
We are sure that there is no one who will not read Clausius "On the Steam-Engine" with much greater ease for having previously read this little book of 312 pages. The foundations of thermodynamics are laid in a simple way; and the chapters on intrinsic energy, on radiation, and on viscosity, are models of their kind.
It is, indeed, to Prof. Maxwell that we owe a beautiful essay on this last subject, mathematical in form, which is printed in the proceedings of the Royal Society. There is also in this volume a discussion of the molecular constitution of bodies, which contains much that is valuable, particularly as an introduction to the various advanced essays on the same interesting topic.
The volume is of a handy size, and is fairly well printed, and there are fewer blemishes in it than in any other of its kind. We notice on pages 139, 152, and 183 (second edition), a looseness which a little more care might have avoided.
On page 139, the author, in speaking of Carnot's reversible engine, says, "It is of a species entirely imaginary, one which it is impossible to construct, but very easy to understand;" thus putting it as a theoretical device solely, as he ought. Again, on page 152 our author proves, or intends to prove, that this engine has a greater efficiency than any other engine, which he attempts to do by an appeal to ordinary experience, which he cites to show that no real working engine "can convert the entire heat of its parts into work," even if this engine consists in part of the theoretical Carnot reversible engine. Now, he has not proved this of any engine, except of those actually in use, and he has expressly declared, as above, that the Carnot engine cannot be made: so that his proof falls to the ground. And, to make matters worse, on page 183 he says: "If we possessed a perfect reversible
