154 • Aecount of Professor Carlini's 



measure of the intensity of gravitation ; i. e. of the excess of 

 the force of gravity over the centrifugal force. In consequence 

 of the ellipticity of the earth, and of the difference in the 

 direction of the two forces, the intensity of gravitation varies 

 according to the different latitudes. It also varies, in the same 

 latitude, according to the greater or less elevation of the pen- 

 dulum above the level of the sea ; i. e. according to its greater 

 or less distance from the centre of the attracting force, foa '^Blt 



Had the earth a perfectly level surface, such, for instance, 

 as it would have if it were everywhere covered by a fluid, the 

 force of gravity, in receding from the surface, would diminish 

 in the duplicate proportion of the distance from the earth's 

 centre. In the actual state of the globe, however, its conti- 

 nents and its islands are raised above the general level of the 

 sea by which it is only partially covered ; and if a pendulum 

 be raised, on the surface of the land, to a known elevation 

 above the sea, the diminution of gravity will not be, as in the 

 more simple case, proportioned to the squares of the respective 

 distances from the earth's centre, but that proportion will 

 require to be modified, by taking into account the attraction of 

 the elevated materials, interposed between the general surface 

 and the place of observation. 



When pendulums are employed in different latitudes, to 

 obtain the ratio of gravitation between the equator and the pole, 

 for the purpose of deducing the ellipticity of the earth, all the 

 places of observation, being on land, are more or less elevated 

 above the sea; inland stations, in particular, are sometimes at 

 considerable elevations: to render these results comparable 

 one with another, it is necessary to reduce each result to what 

 it would have been, had it been made at some level common to 

 all the experiments ; and the surface of the sea has hitherto 

 been taken as that common level. Previous to the publication 

 of a paper of Dr. Young's in the Philosophical Transactions 

 for 1819, the consideration which we have mentioned, that of 

 the attraction of the matter interposed between the place of 

 observation and the level of the sea, was generally unheeded 

 in estimating the allowance to be made for the reduction of 

 different heights to the common level : in that paper, however. 

 Dr. Young took occasion to point out the probable effect of 



