24 MAGNITUDE, FIGURE, AND 



the mode of applying them to this question, and sagaciously 

 remarked, that this method lias a great advantage which 

 detached measurements of degrees and pendulum experi- 

 ments cannot have, in giving in a single result the 

 mean figure of the Earth (or the form belonging to the 

 entire planet). I recall with pleasure the happy expressions 

 by which this method was characterised by its inventor, ( 10 ) 

 "that an astronomer, without quitting his observatory, 

 might learn from the motions of a single heavenly body the 

 precise form of the Earth which he inhabits." According 

 to a final revision of the inequalities in latitude and 

 longitude of our satellite, and the employment of several 

 thousand observations by Burg, Bouvard, and Burckhardt,( n ) 

 Laplace found for the figure of the Earth an ellipticity of 

 g-J-g-th, which approximates very nearly to that given by the 

 measurements of degrees, viz. -^-9. 



The oscillations of a pendulum offer a third method of 

 determining the figure of the Earth (i. e. the ratio of the 

 major to the minor axis, under the assumption of the form 

 being that of an elliptic spheroid), by finding the law 

 according to which the force <jf gravity increases in pro- 

 ceeding from the equator to the poles. The oscillations of 

 a penduhm had been first applied to the determination of 

 time by the Arabian astronomers, and in particular by 

 Ebn-Junis, at the end of the tenth century, in the brilliant 

 period of the Abasside Caliphs ; ( 12 ) and after being neglected 

 for six centuries, were again employed by Galileo and by 

 Kiccioli at Bologna. ( 13 ) . By combination with wheel-work 

 for regulating the march of time-pieces (employed first in 

 the imperfect attempts of Sanctorius at Padua in 1612, and 

 subsequently in the finished work of Huygens in 1656), the 



