We have, then, 39.1154−39.0992 = ·0162 inch., as the [p158] measure of the difference in the intensity of gravitation at the place of observation elevated 1943 metres; and at the level of the sea. The radius of the earth, being 6,376,478 metres, this measure, according to the duplicate proportion of the distances from the earth’s centre, should be ·0238 inch. The attraction of the mountain is, then, equal to ·0238−·0162 = ·0076 inch. Whence it appears that, in this particular instance, the correction for the elevation is reduced, by the attraction of the interposed matter, 68/100ths, or to about 7/10ths of the amount immediately deducible from the squares of the distances. It is obvious that, if we possessed a correct knowledge of the density and arrangement of the materials of which Mont Cenis is composed, so as to enable a computation of the sum of all the attractions which they exercise on the place of observation, this result might furnish, as well as Dr. Maskelyne’s experiments on the deviation of the plumb-line produced by the attraction of Mount Schehallien, a certain determination of the mean density of the earth. Professor Carlini considers that the form of the eminence may be sufficiently represented by a segment of a sphere, a geographical mile in height, having as its base a circle of 11 miles diameter, the distance from Susa to Lansleburgo; the attractive force, on a point placed on the summit, would, in such case, be equal to 2 π δ (1 − (2/3) √(1/11)) or in numbers to 5·020 δ, δ being the density of the mountain, and 2 π the ratio of the circumference to radius. The attractive force of the earth, on a point at its surface, is (4/3) π r Δ, = 14394 Δ, _r_ being the radius of the earth = 3437 geographical miles, and Δ its mean density. Now these two quantities, 14394 Δ and 5·020 δ, should be, to each other, in the proportion of 39.1154,—the pendulum at the level of the sea, representing gravitation at the surface of the earth,—to ·0076, the portion of gravitation at the summit of the mountain due to the attraction of the mountain. By the observations of M. de Saussure and other geologists, Mont Cenis is chiefly composed of schistus, marble, and gypsum; the specific gravities of which substances were ascertained, from numerous specimens in the possession of M. Carlini, to be respectively as follows:— [p159] The schistous 2·81. The marble 2·86. The gypsum 2.32. In the absence of a precise knowledge of the quantity and position or each of these three component parts, we may take the mean, 2.66, of their several densities as approximatively the density of the mountain, = δ. We have then 5.02 δ × 39.1154 Δ = -------------- = 4.77, 14394 × ·0076 a result differing little from that of Cavendish as recently corrected by Dr. Hutton, and still less from that of the Schehallien experiments.