Mr. Ivory on the Ellipticity of the Earth. 165 



The quantities may be arranged in the following manner : 



XXVII. On the Ellipticity of the Earth as deduced from. Ex- 

 periments with the Pendulum. By J. Ivory, M.A. F.R.S.* 



TN the Conn, des Terns 1830, lately published, there is a no- 

 -*- tice of experiments made with an invariable pendulum, by 

 M. Duperrey, in the course of a voyage round the world. The 

 places of observation are not numerous, and one only, namely, 

 Toulon, is a new station. But, in the present state of this in- 

 quiry, no less instruction is to be reaped from the repetition 

 of the experiments at the old stations, than from the extension 

 of our knowledge by new observations. If we could com- 

 pare the lengths of the pendulum determined by different ob- 

 servers on the same spot, the errors to which such experi- 

 ments are liable would become known, and we should be able 

 to estimate the degree of precision with which the figure of 

 the earth can be investigated by this mode of experimenting. 

 An attentive examination of all that has been accomplished in 

 this research will clearly prove that the high expectations of 

 accuracy which were at first entertained from it, have not been 

 realized in practice. It is remarkable that the pendulum-ex- 

 periments within 30° of the equator are very irregular ; while 

 in higher latitudes, if we except Drontheim, the results ob- 

 tained are not chargeable with inconsistency in any great de- 

 gree. Two causes only can be imagined in order to account 

 for the irregularity near the equator : either the experiments 

 must be erroneous, or gravity must be very unequally distri- 

 buted in that quarter of the globe f. 



* Communicated by the Author. 



f Captain Sabine's experiments have lately appeared in this Journal, 

 corrected from an error in estimating the divisions of the level of his re- 

 peating circle. The corrections are excessively trifling, so much so that it 

 seemed hardly worth while to call the attention of the public to the cir- 

 cumstance, as the experiments must be considered as remaining in statu quo. 

 That very great irregularity prevails in these experiments, and indeed in 

 all those made near the equator, is a fact that all will allow ; but the cause 

 has not been ascertained in a satisfactory manner. 



The 



