subject by briefly showing his mode of studying the various paces of the horse. The volume deals systematically and thoroughly with this whole subject, and is full of novelty and curious interest. Prof. Marey's elucidation of the mechanism of flight in birds and insects is one of the most exquisite pieces of experimental investigation that modern science affords. The fertility of his devices, by which the varied results are brought out in all their exactness to the eye, by the graphic method of illustration, is a source of constant surprise to the reader. He makes pictures of all his facts and laws. Of course the value of such investigations stands upon their own scientific merits, but they have a peculiar attractiveness as connected with the phenomena of life in which we are all concerned. Yet there can be no greater mistake than to suppose that such researches are destitute of practical utility. Upon this point Prof. Marey has the following excellent remarks in his introduction:
"The comparison of animals with machines is not only legitimate, it is also extremely useful from different points of view. It furnishes a valuable means of making the mechanical phenomena which occur in living beings understood, by placing them beside the similar but less generally known phenomena which are evident in the action of ordinary machines. In the course of this book, we shall frequently borrow from pure mechanics the synthetical demonstrations of the phenomena of animal life. The mechanician, in his turn, may derive useful notions from the study of Nature, which will often show him how the most complicated problems may be solved with admirable simplicity.
"It is easy to demonstrate the importance of such a subject as locomotion, which, under its different forms, terrestrial, aquatic, and aerial, has constantly excited interest. Whether man has endeavored to utilize to the utmost his own motive power, and that of the animals; whether he has sought to extend his domain, to open a way for himself in the seas, or rise into the air, it is always from Nature that he has drawn his inspirations. We may hope that a deeper knowledge of the different modes of animal locomotion will be a point of departure for fresh investigations, whence further progress will result.
"Every scientific research has a powerful attraction in itself; the hope of reaching truth suffices to sustain those who pursue it, through all their efforts; the contemplation of the laws of Nature has been a great and noble source of enjoyment to those who have discovered them. But to humanity, science is only the means, progress is the aim. If we can show that a study may lead to some useful application, we may induce many to pursue it, who would otherwise merely follow it from afar, with the interest of curiosity only. Without pretending to recapitulate here all that has been gained by the study of Nature, we shall endeavor to set forth what may be gained by studying it still further, and with more care.
"If we knew under what conditions the maximum of speed, force, or labor, which the living being can furnish, may be obtained, it would put an end to much discussion, and a great deal of conjecture, which is to be regretted. A generation of men would not be condemned to certain military exercises which will be hereafter rejected as useless and ridiculous. One country would not crush its soldiers under an enormous load, while another considers that the best plan is to give them nothing to carry. We should know exactly at what pace an animal does the best service, whether he be required for speed, or for drawing loads; and we should know what are the conditions of draught best adapted to the utilization of the strength of animals.
"It is in this sense that progress is being made; but, if we complain with reason of its slow advance, we must only blame our imperfect notion of the mechanism of locomotion. Let this study be perfected, and then useful applications of it will soon ensue.
"Man has been manifestly inspired by Nature in the construction of the machinery of navigation. If the hull of the ship is, as it has been justly described, formed on the model of the aquatic fowl, if the sail has been copied from the wing of the swan inflated by the wind, and the oar from its webbed foot as it strikes the water, these are but a small part of Nature's loans to art. More than two hundred years ago,
