made with an invariable pendulum. 221 
stating that, occupied as I was with professional duties, it 
would have been hopeless to have undertaken these experi- 
ments, without the zealous assistance of a person who, besides 
being free to attend exclusively to the subject, was thoroughly 
skilled in all its details. j remain, my dear Sir, 
most sincerely yours, 
BASIL HALL. 
APPENDIX. 
Being desirous of presenting an account of these operations 
to the Royal Society before the vacation, I had not time to re- 
peat the experiments in London before the above letter was 
read. Since that period, however, I have ascertained, by 
careful observations, that the number of vibrations made by 
the pendulum now, does not accord with that which resulted 
from the experiments made in London before the voyage. By 
a reference to the additional Tables in the Appendix, page 
285* to 288,* and the Remarks which follow, the amount of 
this discordance will be seen, as well as the explanation of 
the cause. It is only necessary to mention here that the 
ellipticities, printed in the above letter, have all been recom- 
puted on the principle stated in the remarks alluded to. 
Abstract of the most exact results at each station. 
Stations. 
Diminution of Gravity 
from Pole to Equator. 
Ellipticity. 
Length of Equat. 
Pend. 
o 1 II 
Galapagos, o 32 N 
,0051412 
I 
284,98 
39,017196 
San Bias, . 21 30 25 N 
,005461 I 
I 
3 1 3»5 5 
39,00904 
Rio, . . 22 55 22 S 
,0053431 
I 
302,37 
39,01206 
B. H. 
London, SOth August, 1823 . 
