Popular Science Monthly/Volume 1/August 1872/Literary Notices

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Theory of Heat. By J. Clerk Maxwell, M.A., F.R.S. D. Appleton & Co.

It is only recently that the general public has been admitted to a knowledge of the researches which are carried on by the leading physicists of the world. Perhaps an educator would consider the desire of the public to be so admitted one of the most encouraging signs of the times, and he undoubtedly would hail the fellowship of the scientists and their audiences as a good omen. It is a very interesting phenomenon which we are now called upon, almost daily, to witness—this affiliation of the student and the public; and it has many good features, as well as some bad ones. Among the good there are the obvious ones of the acquisition of mere knowledge, of the acquaintance with the rigid and exacting logic of the physicists, of the perception of the real beauty in the order and harmony of Nature, and the familiarity with daring thought which stops short of wild speculation, and displays that poise of intellect which is a striking characteristic of the modern school. And, so far, we have noticed only 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 engine and a refrigerator at the absolute zero of temperature, we might convert the whole of the heat which escapes from the body into mechanical work." On pages 99 and 100 we have a similar carelessness, in the use of the term strain: this is defined on page 99 to mean "the alteration of form of any body;" while on page 100 he speaks of the "product of the strain into the average value of the stress," i. e., of the product of a force into a change in shape, which of course is a misnomer, and could be corrected by interpolating the phrase in any direction after "strain."

There are but few of even such errors as these, and we must welcome the book as a most valuable one, in which the golden mean between too great simplicity and too great difficulty is admirably kept; and in the name of the ordinary student we are thankful to Prof. Maxwell for his most admirable essay.E. S. H.

How Plants behave. By Asa Gray. New York: Ivison, Blakeman & Taylor.

Fourteen years ago, Prof. Gray published a little school-book, entitled "How Plants grow," which was designed as a first step, for young people and common schools, of his excellent series of botanical text-books. The present volume of forty-six pages, "How Plants behave," is Part II., or a continuation of "How Plants grow," and is devoted to a description of certain remarkable actions and effects in the vegetable kingdom which are open to familiar inspection. The author's object in the preparation of these little works is thus stated in his preface:

"That young people, that all students, indeed, should be taught to observe, and should study Nature at sight, is a trite remark of the day. But it is only when they are using the mind's eye as well, and raising their conceptions to the relations and adaptations of things, that they are either learning science or receiving the full educational benefit of such a study as Botany or any other department of Natural History.

"There is a study of plants and flowers admirably adapted, while exciting a lively curiosity, to stimulate both observation and thought, to which I have long wished to introduce pupils of an early age. The time has now arrived in which I may make the attempt, and may ask young people to consider not only, 'How Plants grow,' but how plants act in certain important respects, easy to be observed—everywhere open to observation, but (like other common things and common doings) very seldom seen or attended to. This little treatise, designed to open the way for the young student into this new, and, I trust, attractive field, may be regarded as a supplement to the now well-known book, the title of which is cited at the beginning of this prefatory note. If my expectations are fulfilled, it will add some very interesting chapters to the popular history of plant-life.

"Although written with a view to elementary instruction, and therefore with all practicable plainness, the subjects here presented are likely to be as novel, and perhaps as interesting, to older as to young readers."

Prof. Gray has well succeeded in his purpose, and the pages of his little book are full of interest to all who care for the curiosities of the vegetable world. His volume is divided into three chapters. The first shows how plants move and climb and take positions; the second tells how plants employ insects to work for them; and the third describes how certain plants capture insects. Among all the surprising effects presented by natural objects, none are more curiously interesting than the habits and adaptations of vegetable structures, and Prof. Gray tells the story in his own clear and graphic way. The pages of his little book are full of pleasant information, and cannot fail to be instructive; and, if the pupils are attracted to go beyond its pages to examine for themselves the structures and actions described, the experience will be invaluable as a cultivation of the observing powers.