xv NOTES. 



secundi arclietypus, mensurse naturalis exemplar, utiiiara universalis !" Prom 

 what La Condamiue has said, in his Journal du Voyage a 1'Equateur, 1751, 

 p. 163, respecting parts of the inscription which are not filled up, and a dif- 

 ference between Bouguer and himself about the numbers, I had conjectured 

 that I should find considerable discrepancy between the tablet and the inscrip- 

 tion as published in Paris ; but, after a careful comparison, I discovered only 

 two discrepancies of little importance, "ex area graduum 3," instead of 

 " ex arcu graduum plus ptam trium;" and the date of "1745," instead of 

 ' 1742." The date of 1745 is singular, because La Condamine returned to 

 Europe in 1744, Bouguer in June of the same year, and Godin left South 

 America in July 1744. The most necessary and useful amendment of the 

 numbers of the inscription would have been the astronomical longitude of 

 Quito. (Humboldt, Recueil d'Observ. astron. T. ii. pp. 319 354.) Nouet's 

 latitudes, engraved on Egyptian monuments, offer a more recent example of 

 the danger of perpetuating, thus solemnly, erroneous or imperfectly computed 

 results. 



( 132 ) p. 158. On the increased intensity of gravitation in volcanic islands 

 (St. Helena, Ualan, Fernando de Noronha, Isle of France, Guam, Mowi, and 

 the Galapagos), Rawak (Liitke, p. 240) being an exception, perhaps, on 

 account of its proximity to the high land of New Guinea, see Mathieu, in 

 Delambre, Hist, de FAstronomie au 18 me siecle, p. 701. 



[The fact of the increased intensity of gravitation in volcanic islands was, 

 I believe, first made known by myself (Pendulum Experiments, 1825, pp. 

 237 341), as the results of my own experiments at the islands of Ascension 

 and of St. Thomas (in the gulph of Guinea), and at other stations of 

 different geological character. The comparison of the whole series furnished 

 a numerical scale of local influence in which the volcanic islands of Ascension 

 and St. Thomas occupied the higher extremity, and stations of alluvial soil 

 and sand the lower extremity, whilst the intermediate gradations of local 

 influence were seen to correspond in a remarkable manner with the density of 

 the superficial strata. " The scale afforded by the pendulum for measuring 

 the intensities of local attraction appears to be sufficiently extensive to render 

 it an instrument of possible utility in inquiries of a purely geological nature. 

 It has been seen that the rate of a pendulum may be ascertained with proper 

 care to a single tenth of a second per diem ; whilst the variation of rate occa- 

 sioned by the geological character of stations has amounted in extreme case* 

 to nearly ten seconds per diem : a scale of 100 determinate parts is thus 

 afforded in which the local attraction dependent on the geological accidents 



