158 Account of Professor Carlini's 



measure of the difF^ence 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, to -j^^ths, or to about ^ths of the 

 amount immediately deducible from the squares of the dis^ 

 tances. 



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 experi^ 

 ments on the deviation of the plumb-line produced by the 

 attraction of Mount Schehallien, a certain determination of thei 

 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 'r ^ (1— f^ -^)^ 

 or in numbers to 5 -020 J, ^ being the density of the mountain, 

 and 2 ir the ratio of the circumference to radius. The 

 attractive force of the earth, on a point at its surface, is f tt r A , 

 = 14394 A J r being the radius of the earth =r 3437 geogra- 

 phical miles, and a its mean density. Now these two quan- 

 tities, 14394 A and 5 ♦ 020 ^, should be, to each other, in the 

 proportion of 39.1] 54, — ^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 com- 

 posed of schistus, marble, and gypsum ; the specific gravities 

 of which substances were ascertained, from numerous speci- 

 mens in the possession of M. Carlini, to be respectively as 

 follows : — 



