FIGURE OF THE EARTH. 167 



Galileo, who first observiid when a boy (having, probably, 

 suffered his thoughts to wander from the service) that the 

 height of the vaulted roof of a church might be measured by 

 the time of the vibration of the chandeliers suspended at dif- 

 ferent altitudes, could hardly have anticipated that the pendu- 

 lum would one day be carried from pole to pole, in order to 

 determine the form of the Earth, or, rather, that the miequal 

 density of the strata of the Earth affects the length of the sec- 

 onds pendulum by means of intricate forces of local attraction 

 which are, however, almost regular in large tracts of land. 

 These geognostic relations of an instrument intended for the 

 measurement of time — this property of the pendulum, by 

 which, like a sounding line, it searches unknown depths, and 

 reveals in volcanic islands,* or in the declivity of elevated con- 

 tinental mountain chains,t dense masses of basalt and mela- 



archetypus, mensurce naturalis exemplar, utinam universalis t From an 

 observation made by La Condamiue, in his Journal du Voyage a V Eqiia- 

 teur, 1751, p. 163, regarding parts of the inscription that were not filled 

 up, and a slight difference between Bouguer and himself respecting the 

 numbers, I was led to expect that I should find considerable discrepan- 

 cies between the marble tablet and the inscription as it had been de- 

 scribed in Paris; but, after a careful comparison, I merely found two 

 perfectly unimportant differences: "ex arcu graduum 3i^" instead of 

 "ex arcu graduum plusquam trium," and the date of 1745 instead of 

 1742. The latter circumstance is singular, because La Condamine re- 

 turned to Europe in November, 1744, Bouguer in June of the same year, 

 and Godin had left South America in July, 1744. The most necessary 

 and useful amendment to the numbers on this inscription would have 

 been the astronomical longitude of Quito. (Humboldt, Recueil d] Oh' 

 serv. Astron., t. ii., p. 319-354.) Nouet's latitudes, engraved on Egyp- 

 tian monuments, offer a more recent example of the danger presented 

 by the grave perpetuation of false or careless results. 



* Respecting the augmented intensity of the attraction of gravitation 

 in volcanic islands (St. Helena, Ualan, Fernando de Noronha, Isle of 

 France, Guam, Mowi, and Galapagos), Rawak (Lutke, p. 240) being 

 an exception, probably in consequence of its proximity to the high 

 land of New Guinea, see Mathieu, in Delambre, Hist, de VAstronoinie, au 

 I8i»e Steele, p. 701. 



t Numerous observations also show great irregularities in the length 

 of the pendulum in the midst of continents, and which are ascribed to 

 local attractions. (Delambre, Mesure de la Miridienne, t. iii., p. 548; 

 Biot, in the M6m. de V Acad6mie des Sciences, t. viii., 1829, p. 18 and 

 23.) In passing over the South of Fi'ance and Lombardy from west to 

 east, we find the minimum intensity of gravitation at Bordeaux; from 

 thence it increases rapidly as we advance eastward, through Figeac, 

 Clermont-Ferrand, Milan, and Padua ; ai'id in the last town we find that 

 the intensity has attained its maximum. The influence of the southern 

 declivities of the Alps is not merely dependent on the general size of 

 their mass, but (much more), in the opinion of Elie de Beaumont (Rech. 

 tur les R6vol. de la Surface du Globe, 1830, p. 729), on the rocks of 

 melaphyre and serpentine, wl" rh have elevated the chain. On the 



