324? Mr. Ivory on the Ellipticity of the Earth 



Now the numbers in this Table should be nearly equal, if the 

 seven experiments were consistent, and belonged to the same 

 elliptical figure. This, however, is so far from being the case, 

 that we may discern three different systems in the lengths it 

 contains. One derived from the experiments at Ascension 

 and St. Thomas, having an equatorial pendulum about 39*02 ; 

 another with an equatorial pendulum about 39*015, compre- 

 hending Bahia, Sierra Leone, and Jamaica ; and a third com- 

 prehending Maranham and Trinidad, with an equatorial nearly 

 equal to 39*0117. If we adopt the last determination and 

 combine it with the experiments at the stations of the Trigo- 

 nometrical Survey in Great Britain, we shall obtain an ellipti- 

 city very little different from that generally received; if we 

 prefer the second and combine it in the same manner, the re- 

 sulting ellipticity will be very nearly the same with what Cap- 

 tain Sabine has deduced from his calculations; and lastly, if 

 we combine the first equatorial pendulum, namely 39*02, with 

 the same experiments, we shall get an ellipticity still greater 

 than that assigned by Captain Sabine. But it may be said 

 that we ought to adopt the mean equatorial pendulum, re- 

 sulting from all the seven experiments, in preference to any of 

 the three particular systems above-mentioned. Now this will 

 be found to make the pendulum at the equator about 39*0156, 

 which is hardly different from the second of the foregoing 

 lengths, and almost coincides with the result which Captain 

 Sabine has uniformly deduced from all the combinations of 

 his experiments. 



The observations that have been made unvail the whole 

 mystery of Captain Sabine's investigations. They disclose the 

 real reason of that uniformity and consistency of result which 

 are preserved in calculations apparently greatly varied, and 

 which constitute the grand argument in support of the pro- 

 posed ellipticity. It must be observed, that Captain Sabine 

 has employed no tropical experiments except his own, and 

 that these are a constituent part in all his calculations. Now 

 it requires very little sagacity to discover that the results he 

 obtains can be very little different from what they would be, if 

 the mean of the equatorial pendulums was immediately com- 

 bined with the northern experiments. It happens that, if we 

 except Drontheim, the experiments at the northern stations 

 are tolerably consistent; and hence it follows that nearly the 

 same ellipticity is brought out in every calculation which in- 

 cludes all the tropical pendulums. Although, therefore, there 

 is a multiplicity of arithmetical operations, there is no accu- 

 mulative evidence in favour of the result. The same ellipti- 

 city is always found, because it may be affirmed that a prin- 

 cipal 



