30 COSMOS. 



of the bulging which would be yielded by a polar compres- 

 sion of - 



As soon as it had been ascertained by more accurate mea- 

 surements of a degree, made at very different latitudes, that 

 the earth could not be uniformly dense in its interior, (because 

 the results showed that the compression was very much 

 less than had been assumed by Newton (-^o"), an( ^ much 

 greater than was supposed by Huygens (-5^), who con- 

 sidered that all forces of attraction were combined in the 

 centre of the earth,) the connection between the amount 

 of compression and the law of density in the interior of our 

 earth necessarily became a very important object of ana- 

 lytical calculation. Theoretical speculations regarding gravity 

 very early led to the consideration of the attraction of large 

 mountain masses, which rise freely and precipitously into 

 the atmosphere from the dried surface of our planet. New- 

 ton, in his Treatise of the System of the World in a Popular 

 Way, 1728, endeavoured to determine what amount of 

 deviation from the perpendicular direction the pendulum 

 would experience from a mountain 2,665 feet in height and 

 5,330 feet in diameter. This consideration very probably 

 gave occasion to the unsatisfactory experiments, which were 

 made by Bouguer on Chimborazo, 25 by Maskelyne and 



25 Bouguer who had been induced by La Condamine to institute 

 experiments on the deviation of the plummet near the mountain of 

 Chimborazo, does not allude in his Figure de la Terre, pp. 364 394 

 to Newton's proposition. Unfortunately the most skilful of the two 

 travellers did not observe on the east and western sides of the 

 colossal mountain, having limited his experiments (December, 1738) to 

 two stations lying on the same side of Chimborazo, first in a south- 

 erly direction 61 30' West, about 4,572 toises or 29,326 feet from 

 the centre of the mountain, and then to the South 16 West (distance 

 1,753 toises or 11,210 feet). The first of these stations lay in a district 

 with which I am well acquainted, and probably at the same elevation 

 as the small alpine lake of Yana-cocha, and the other in the pumice-stone 

 plain of the Arenal (La Condamine, Voyage d I'Equateur, pp. 68 70). 

 The deviation yielded by the altitudes of the stars, was, contrary to all 

 expectation, only 7. "5 which was ascribed by the observers themselves 

 to the difficulty of making observations so immediately in the vicinity 

 of the limit of perpetual snow, to the want of accuracy in their instru- 

 ments, and above all to the great cavities which were conjectured to 

 exist within this colossal trachytic mountain. I have already expressed 

 many doubts, based xipon geological grounds, as to this assumption of 

 very large cavities, and of the very inconsiderable mass of the tra- 



