480 



posed of materials of various densities, the pendulum 

 may be expected to indicate such variations with very 

 considerable precision." The opinion thus expressed 

 was considered by me to be so strikingly confirmed by 

 the systematic character of the " anomalies" (as they 

 were then called) at the equatorial and polar stations of 

 my experiments in 1821-1822, as to justify the inference 

 (Pend. Expts. 1825, p. 341,) that "the scale afforded by 

 the pendulum for measuring the intensities of local 

 attraction appears to be sufficiently extensive tc render 

 it an instrument of possible utility in inquiries of a 

 purely geological nature. The rate of a pendulum 

 may be ascertained, by proper care, to a single tenth of 

 a vibration per diem ; whilst the variation of jate, oc- 

 casioned by the geological character of two stations, has 

 amounted, in extreme cases, to nearly ten vibrations per 

 diem : a scale of 100 determinable parts is thus afforded, 

 in which the local attraction dependent on the geolo- 

 gical accidents may be estimated." The inference thus 

 drawn was illustrated by a table (p. 338), exhibiting the 

 general nature of the surface-strata at the thirteen sta- 

 tions which I had visited in 1821-1822, with the excess 

 or defect at each station of the rate of the pendulum sup- 

 posed to be occasioned thereby, and the value correspond- 

 ing to the excess or defect in the scale of 100 parts; as 

 well as by a similar table (p. 345) for nineteen stations, 

 including those of Captain Kater. These were, I believe, 

 the first tables of the kind that were published. It is 

 chiefly to such local influences that we must ascribe the 

 discordances that have appeared in the ellipticity derived 

 from stations too few in number and too near each other 

 in latitude. If no irregular attraction occurred, the 



