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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.



Death of Dr. Stimpson.—In the recent death of Dr. William Stimpson, secretary of the Chicago Academy of Sciences, American science has suffered an irreparable loss. He was born near Boston, February 14, 1832, and was drawn by a strong impulse to the study of science in his boyhood. His