Dr. Chladni made many curious experiments on the figures assumed by sand and similar substances, when strewed over vibrating sonorous bodies. The reader may easily try an experiment of this kind. Let a square piece of glass be taken, such as that used for windows, not less than four or five inches over, the edges of which are to be smoothed by grinding. Spread over the plate, as evenly as possible, a little sand, and, holding it between the thumb and fore-finger, in the middle, pass the bow of a violin against one of its edges, drawing it either upwards or downwards, in a direction perpendicular to its surface. A tremulous motion will be immediately observed, and the sand will assume some particular and fixed figure. If the bow be passed over the middle of one of the sides, the sand will arrange itself in the direction of the two diagonals, dividing the square into four isosceles triangles. If the bow be applied at any point which is one-fourth the length of the square from any angle, the arrangement of the sand will represent the two diameters of the square, dividing it into four equal figures of the same form. If the square be held at the two extremities of either diameter, and the bow be applied to the extremities of the other diameter, the sand will take the figure of an oval, having its major axis in the same direction as one of the diameters. Other experiments of the same kind have since been made by M. Voigt, and also by the celebrated Oersted. The latter covered a plate of metal or glass with the lycopodium seed, or the seed of the club-moss, instead of sand; he then tried to produce a sound in the manner of Chladni, and instantly he saw the dust distribute itself into a number of little regular tumuli, which put themselves in motion at their extremities, or formed the figures discovered by this naturalist. They always ranged themselves in the form of a curve, the convexity of which was in proportion to the point touched by the violin bow, or towards the point which has an analogous situation; the nearer that each of these little heaps was to these points, the greater was its height, a circumstance which gave remarkable regularity to the figure. The interior of the small elevations thus obtained, were in constant motion during the continuance of the sound, and the duration of the vibrations might be observed on a plate from four to six inches in diameter. At one moment the height increased, at another it diminished, and the dust had the appearance of arranging itself in small globules, which rolled one above another.