at the Island of Balta, and at Woolwich Common. . 439 
quiry, I would most earnestly recommend that proper persons be 
appointed to make experiments with pendulums, not only in dif- 
ferent places on the same meridian, or in widely differing lati- 
tudes; but in various places upon or near the same parallels of 
latitude. Experiments of this kind can be made with more fre- 
quency and conducted with less expense, than any other class of 
operations for determining the figure of the earth; and they 
would not only be subservient to the determination of that figure, 
generally, but would furnish by their local anomalies ready indi- 
cations of geological peculiarities, which might not previously 
have been detected by geologists themselves. That every possi- 
ble satisfaction might result from these experiments, it would 
be adviseable that at each station they should be conducted si- 
multaneously, by three, or at least two distinct classes of ap- 
paratus, and by separate observers. It was on a high estimate 
of the advantages of simultaneous operation at the same place by 
means of different instruments and observers, that I anxiously en- 
gaged in the experiment in the Zetland isles. While I regret 
that M. Biot, by quitting the Balta station, and by declining to 
make a regular exchange of records of the respective experiments, 
precluded us from realizing this species of benefit; I have the 
satisfaction of feeling that the occasion of the separation cannot 
correctly be imputed, either to myself or to Captain Colby, my 
indefatigable and liberal-minded associate in that expedition. 
— 
_ This paper might now terminate, were it not that an acci- 
dental circumstance, the tendency of which to introduce error 
has been most industriously and ungenerously utisrepresented, 
and made the basis of an illiberal comparison between the accu- 
racy of my experiment ana that of M. Biot, by persons who have 
not taken the trouble to ascertain facts—renders it expedient 
that I should present them here. 
There being uo observatory at the Royal Military Academy in 
1817, the * rate”’ of the clock was ascertained by the Rev. Lewis 
Evans, at his private observatory on Woolwich Common, in the 
spring of that year. The rate was found to keep generally be- 
tween ‘3 and +9 of asecond, the mean being, nearly, +°44; and 
on April 14, 1817, the cloc k, pendulum, and bob, were carefully 
packed up in their respective cases. I was not present at the 
packing, because at that time it was not determined that I should 
for a season qnite my official duties at Woolwich, for the pur- 
pose of assisting in the proposed operations in the north. Col. 
Mudge and M. Biot started for Edinburgh early in May ; and on 
June 2th I joined them at Leith. On my arrival there I found 
Col. Mudge too ill to render it possible for him to accompany 
us further northward, or indeed to give any specific directions as 
Ee4 to 
