THE FIGURE OF THE EARTH. 33 



the earth could not be uniformly dense in its interior (be- 

 cause the results showed that the compression was very- 

 much less than had been assumed by Newton (-jto)? and 

 much greater than was supposed by Huygens (^-s)? who 

 considered 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 analyt- 

 ical 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. Newton, 

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

 1728, endeavored to determine what amount of deviation 

 from the perpendicular direction the pendulum would experi- 

 ence from a mountain 2665 feet in height and 5330 feet in 

 diameter. This consideration very probably gave occasion 

 to the unsatisfactory experiments which were made by Bou- 

 guer on Chimborazo,* by Maskelyne and Hutton on She- 

 ll allien, near Blair- Athol, in Perthshire ; to the comparison 

 of pendulum lengths on a plain lying at an elevation of 6000 



* 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, p. 364-394, to 

 Newton's proposition. Unfortunately the most skillful of the two trav- 

 elers 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 southerly di- 

 rection 61° 30' West, about 4572 toises, or 29,326 feet, from the centre 

 of the mountain, and then to the South 16° West (distance 1753 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 a VEquateur, p. 68-70). The 

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

 pectation, only 1" -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 ex- 

 pressed many doubts, based upon geological grounds, as to this as- 

 sumption of very large cavities, and of the very inconsiderable mass 

 of the trachytic dome of Chimborazo. South-southeast of this mount- 

 ain, near the Indian village of Calpi, lies the volcanic cone of Yana- 

 urcu, which I carefully investigated in concert with Bonpland, and 

 which is certainly of more recent origin than the elevation of the 

 great dome-shaped trachytic mountain, in which neither I nor Bous- 

 singault could discover any thing analogous to a crater. See the 

 Ascent of Chimborazo in rav Klein? Schrifte/i, bd. i., s. 138. 



r> -2 



