Page:Popular Science Monthly Volume 6.djvu/462

446 movement of the lever opposite to that described above. Thus the lever records accurately every movement of the membrane of the distant drum, and the intervening flexible tube allows one to attach the drum to the limb of a moving man, or quadruped, to the wing of a flying-bird, or to the chest, to obtain the traces of the motions of the lungs and of the heart.

In 1863 Marey first began to apply the graphic method to biological studies, in his "Physiologie médicale de la Circulation du Sang." In 1868 he published his "Du Mouvement dans les Fonctions de la Vie." In the preface of this truly valuable work he says: "By the use of the graphic method the illusions of the observer, the tediousness of descriptions, and the confusion of facts, disappear. These two ruling qualities, clearness and conciseness, become every day more desirable, by reason of the enormous increase in biological publications." In his last work, "Animal Mechanism," be has illustrated this remark; for surely no "tediousness" will be experienced in the perusal of this work, in which we are taught, with such "clearness and conciseness," how men and quadrupeds walk and run, and how birds and insects fly.

The desire to see Marey's work on Animal Mechanism fully appreciated by the public has induced us to put the reader in possession of his quite recent discoveries, which could not be incorporated in the book published in the "International Series." We refer to two of his most important researches, one on "Human Locomotion," taken from the Comptes Rendus, of July 13, 1874; the other, "On the Resistance of the Air under the Wing of a Bird during its Flight," we take from the Journal de Physique of July, 1874.

—The brothers Weber believed that in human locomotion the oscillation of the leg in walking was due alone to the action of gravity; this is to say, that the foot, while off the ground, has the motion of a pendulum. For a long time this opinion has held its place in physiology, but it has been opposed, in recent years, by arguments of various kinds. First, by M. Duchenne, of Boulogne, who showed that the leg is not entirely passive during its displacement, for certain muscular paralyses prevent its oscillation; M. Giraud-Teulon has attacked the theory of Weber, by showing the mathematical errors on which it is founded; and, finally, M. Carlet has determined, experimentally, the active function of certain muscles in the displacement of the leg during walking.

If gravity does not alone act in producing the oscillation of the leg, it becomes impossible to foresee what motion will result from its combination with muscular action. I have appealed to the graphic method for the experimental answer to this question.

When a body moves in a straight line, with variable velocities at each instant, it is easy to obtain the graphic representation of its motion, provided the space moved over is not too extensive. It