The two accomplishments common to all mankind are walking and talking. Simple as they seem, they are yet acquired with vast labor, and very rarely understood in any clear way by those who practise them with perfect ease and unconscious skill. Talking seems the hardest to comprehend. Yet it has been clearly explained and successfully imitated by artificial contrivances. We know that the moist membranous edges of a narrow crevice (the glottis) vibrate as the reed of a clarionet vibrates, and thus produce the human _bleat_. We narrow or widen or check or stop the flow of this sound by the lips, the tongue, the teeth, and thus _articulate_, or break into joints, the even current of sound. The sound varies with the degree and kind of interruption, as the "babble" of the brook with the shape and size of its impediments,--pebbles, or rocks, or dams. To whisper is to articulate without _bleating_, or vocalizing; to _coo_ as babies do is to bleat or vocalize without articulating. Machines are easily made that bleat not unlike human beings. A bit of India-rubber tube tied round a piece of glass tube is one of the simplest voice-uttering contrivances. To make a machine that _articulates_ is not so easy; but we remember Maelzel's wooden children, which said, "Pa-pa" and "Ma-ma"; and more elaborate and successful speaking machines have, we believe, been since constructed. But no man has been able to make a figure that can _walk_. Of all the automata imitating men or animals moving, there is not one in which the legs are the true sources of motion. So said the Webers[A] more than twenty years ago, and it is as true now as then. These authors, after a profound experimental and mathematical investigation of the mechanism of animal locomotion, recognize the fact that our knowledge is not yet advanced enough to hope to succeed in making real walking machines. But they conceive that the time may come hereafter when colossal figures will be constructed whose giant strides will not be arrested by the obstacles which are impassable to wheeled conveyances. [Footnote A: _Traité de la Méchanique des Organes de la Locomotion_, Translated from the German in the _Encyclopédie Anatomique_. Paris, 1843.] We wish to give our readers as clear an idea as possible of that wonderful art of balanced vertical progression which they have practised, as M. Jourdain talked prose, for so many years, without knowing what a marvellous accomplishment they had mastered. We shall have to begin with a few simple anatomical data.