GLEANINGS IN SCIENCE. 
9 
By this modification, the risk of the mutual influence of the pendulum and the 
clock is avoided. 
4. The disk w as attached to the thread iiy means of knots in the thread itself ; 
avoiding the correction for the small cup usually employed for that purpose. 
5. An alteration was made in the weight and shape of the knife-edge suspen- 
sion ; reducing its weight to about. 10 grains, and giving it the shape of a rotella, 
instead of that, of a triangular prism. 
The simple pendulum and miscroscopes were attached to a strong-wall, in a room 
on the ground floor, contiguous to the temporary observatory, and well sheltered 
from the sun and weather. The clock with winch the pendulum was compared, 
was supported by a pyramid of masonry resting on the ground, and occupying the 
middle of the room. The experimental length between the microscopes was refer- 
red to three standard metres, in perfect agreement with each other ; one received 
from Paris by the commission of weights and measures at Milan ; a second brought 
more recently from Paris by Conte Moseati ; and a third in the possession of the 
Royal Academy of Turin. 
The experiments were commenced on the 3d of September, and terminated on 
the 27th, being interrupted by M. Carlini’s absence at Chambery from the 7th to 
the 12th. The distance between the microscopes, and the oscillations and length 
of the pendulum, were measured alternately. Thirteen independent results were 
thus obtained, of which the greatest discordance from the mean, was not more than 
ioo 3 ooths of a British inch. The mean result was 32,0992 British inches, the 
length of the pendulum vibrating seconds in a vacuum, at the place of observation 
on Mont Cenis, 1943 metres, or B374feet above ihesea, in the latitude of 45" 14' 
10". To compare with this determination, we may obtain a tolerably fair approx- 
imation to the pendulum at the level, of the sea in the latitude of 45° 14’ 10", 
such as its length might have been found, if the mountain could have been remov. 
ed and the pendulum placed on its site, by deduction from the lengths actually 
measured with a similar apparatus, on the arc between Formentera and Dunkirk, 
at stations not far removed from the level of the sea, in the adjacent parallels to 
Mont. Cenis. and in the countries adjoining. Of these there are five, not includ- 
ing the station at Clermont, in consequence of its. great elevation t they are as 
Allows : — 
' Dunkirk 51 02 10 ; its pendulum at the level of the sea =39.13771 
Paris ,. 48 50 14; „ „ „ „ 30.12894 
Bordeaux 44 50 26; ,, „ „ „ 39.11295 
Figeac 41 36 45; „ „ „ „ 30.11212 
Formentera 38 30 56; „ „ „ „ 39.09176 
The mean length of the seconds pendulum at the level of the sea, in the latitude 
of 45“ 1 4' 10", deduced from these determinations, is 39,1154; and it is so equally, 
whether an ellipticity of 5 J s th, or of 5 j.,tli, or any intermediate, ellipticity be 
assumed in tbe reduction. 
We have, then, 39.1154 — 31 099 2— 0102 inch, as the measureofthe differ- 
ence in the intensity of gravitation at the place of observation, elevated 1943 me- 
tres, 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 inter- 
posed matter, to ,’^ths, or to about T 7 B ths 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 arrange- 
ment of the materials of which Mont Cenis is composed, so as to enable a compu- 
tation of the Mini of all the attractions which they exercise on the place of obser- 
vation, 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 Carlijfti con- 
siders 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 2ir o' ( I a v c _c ^ 0T ; n 
numbers to 5'020, 5. $ 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 . it r A , =.4394 A, r being the radius of the earth = 3437 geographical miles. 
