28 COSMOS. 



These observations have confirmed a fact which had been 

 strikingly demonstrated in the northern hemisphere, namely, 

 that the intensity of gravity is not the same for all places 

 having the same latitude, and that the increase of gravity 

 from the equator toward the poles appears to be subjected 

 to different laws under different meridians. Although the 

 pendulum measurements made by Lacaille at the Cape of 

 Good Hope, and those conducted in the Spanish circumnav- 

 igating expedition by Malaspini, may have led to the belief 

 that the southern hemisphere is, in general, much more com- 

 pressed than the northern, comparisons made between the 

 Falkland Islands and New Holland on the one hand, and 

 New York, Dunkirk, and Barcelona on the other, have, 

 however, by their more exact results, shown that the con- 

 trary is the case, as I have already elsewhere indicated.* 



From the above data it follows that the pendulum (al- 

 though it is by no means an unimportant instrument in 

 geognostic observations, being as it were a sort of plummet 

 cast into the deep and unseen strata of the earth) does not 

 determine the form of our planet with the same exactitude 



* Cosmos, vol. i., p. 169. Eduard Schmidt (Mathem. und Phys. Geo- 

 graphie, Th. i., s. 394) has separated from a large number of the pen- 

 Tiulum observations which were made on board the corvettes Descubi- 

 erta and Atrevida, under the command of Malaspina, those thirteen 

 stations which belong to the southern hemisphere, from which he ob- 

 tained a mean compression of -^-g^.-g^. Mathieu obtained tj-;^.^ from 

 a comparison of Lacaille's observations at the Cape of Good Hope and 

 the Isle of France with Paris, but the instruments of measurement 

 used at that day did not afford the same certainty as we now obtain 

 by the appliances of Borda and Kater, and the more modern methods 

 of observation. The present would seem a fitting place to notice the 

 beautiful experiments of Foucault, which afford so high a proof of the 

 ingenuity of the inventor, and by which we obtain ocular evidence of 

 the rotation of the earth on its axis by means of the pendulum, whose 

 plane of vibration slowly rotates from east to west. ( Comphs rendus 

 de VAcad. des Sc; Seance du 3 Fevrier, 1851, t. xxxii., p. 135.) Ex- 

 periments for noticing the deviation toward the east in observations 

 of falling bodies, dropped from church towers or into mines, as sug- 

 gested by Benzenberg and Reich, require a very great height, while 

 Foucault's apparatus makes the effects of the earth's rotation percep- 

 tible with a pendulum only six feet long. We must not confound the . 

 phenomena which may be explained by rotation (as, for instance, 

 ■Richer's clock experiments at Cayenne, diurnal aberration, the devia- 

 tion of projectiles, trade-winds, etc.) with those that may at any time 

 be produced by Foucault's apparatus, and of which the members of 

 the Academia del Cimento appear to have had some idea, although they 

 did not farther develop it (Antinori, in the Comptes rendus^ t. xxxii., 

 p. 635). 



