ON THE ELLIPTICITY OF THE EARTH. 475 



pendulums of precisely the same form and construction 

 as those which had been employed by Captain Kater 

 and myself. Both pendulums were vibrated at all the 

 stations, but from some cause which Mr. Baily was un- 

 able to explain, the observations with one of them were 

 so discordant at South Shetland as to require their re- 

 jection. The acceleration computed from the mean of 

 the two pendulums at all the other stations, and from 

 the one pendulum at South Shetland, gives, according 

 to Mr. Baily's report, pp. 74 and 75, for the increase of 

 gravity from the equator to the pole, '0051924, and for 

 the ellipticity, g 8 * 9 . 2 . The very close agreement of this 

 result with that which had been previously stated from 

 the experiments in the northern hemisphere affords a 

 very strong probability that, in the conclusion common 

 to them both, we have a true measure of the ellipticity 

 of the earth derived by means of the pendulum, as well 

 as a highly interesting and important indication of sym- 

 metry in the two hemispheres. 



There are two circumstances in particular which dis- 

 tinguish the double series of experiments discussed in 

 this note, and may claim for their result a higher degree 

 of confidence than has been accorded to the results of 

 experiments made under less favourable conditions. 

 The first is one which will be readily appreciated as soon 

 as stated, viz., the extent of the arc of the meridian on 

 which the stations of experiment are distributed from 

 62 46' S. to the equator, and from the equator to 

 79 50' N. The second may perhaps be less readily 

 appreciated at the first view; but it is a condition, 

 nevertheless, of primary importance in results whose 

 value is to depend on their strict comparability with 



