Hate of the Southern hemifphere, and can pronounce with
certainty, that the equilibrium, o f the globe is effedlually
preferved,
quantity as that which M. Le Monier refts his whole caufe upon.; and i f fo, his arguments,
which depend wholly on a fuppofition, that not only they, but M . Bouvet*%
alfo, were capable of determining it with the utmoft exa&nefs, mull fall to the
ground. .
lit , It appears, from various inftances, that, the variations obferved by the fame
compafs would difler'30 to 50, 6*, and fomefimes even io °, from no other caufe whatever,
but putting the ihip’s head a contrary way * .
jid, That the fame compafs, in the fame iltuation in every refpe£t, within a few
miles, but at two different times o f the fame day, would give variations differing from
one another, 3*, 40, 50, 6°, and even y° f .
3d, That -the fame compafs, on the fame day, and in the hands o f the fame obferver,
will give variations differing from one another by 5®, on board the fame ihip, when
under fail, and when at anchor in a road->ftead
4th, Compaffes, made by the fame artift, at the fame time and place, but on board
different ihips, differed 30, 40, and even 50 in the variation §.
5th, The fame Compafles, on board the fame ihip, and within a few miles of the
fame lituation, but at different times of our being there, gave variations differing by
40 and 50, or upwards |].
6th, Different
* Seethe Original Agronomical Obfervations, made in the fécond Voyage, March i i
»773* P- 372- January 24, 1774, p. 375. and July 28, p. 3.78.
■ f Obfervations in the fécond Voyage, February 2, 1773, p. 371. and January ig i 77l-
p.382. Alfo Obfervations in laft Voyage, July 17, 1,776, p .1 7 9 . Auguft-^ p. 181. la-
nuary 24, 1777, p. 192. and September 15, 1778, p. 205;. | , - .
X Allronomical obfervations o f fécond Voyage, July 14, 17 7-, p. 385.
I Compare the Allronomical Obfervations, made in the fécond Voyage, Auguft 3 and o
arid September 4, 1772, p. 181. with thofe-of the fame dates, p. 369. Thofe o f Tanuarv
11 , and 14, and February7, 1777, p. 1.82, with thofe o f the fame dates, p. 3 7,. Alfo
Aftronomical Obfervations, made in the laft Voyage, o f December 27 1776 p i g i Fe
W r y « 1 7 7 8 , p. 201. May ; and 8, p. ,,o2. July g, and *4, ,779,' g / ' ani'
i T i l t f ’ P' 2,1 W1 dates’ P- *9 '* 2P ’ *9i , 297,
8 II Compare Aftronomical Obfervations, made in the fécond Voyage, February i-n
p. 37c. with Obfervations o f December .774, p. 38,. Alfo Obfervatibns, m dé
in the laft Voyag-, May 3, and June 18, 1779, p. 20S.
preferved, though th e , proportion of fea actually failed
through, leaves no fufficient fpace for the correfponding
mafs
6th, Different compaffes, at the fame time, on board the fame ihip, and in every '
refpeit under the fame circumftances, will give variations differing from one another,
3°, 4°, 50, and 6° *.
Thefe differences, feveral of which happened very near the place in queflion, are all
o f them at Ieaft equal to, moftof them much gAater, and fome o f them double that
Which M. Le Monier founds his argument on, even according to his own account o f it,
which I have already Ihewn is by ho means admiflible, and, therefore, totally invalidate
it. T o allege that the inftruments made ufe of in Captain Cook’ s two voyages
were bad, -or that the obfervers were not expert in the ufe o f them, wifi anfwer no
purpofe: they are the inftruments and. obfervers which M. Le Monier’% argument
muft reft on; and, therefore, let thofe of the French, or any other navigator, have
been ever fo much' better than they were (which few will be hardy enough to affert, and
fewer ftitl found weak enough to belieye), it will avail nothing to the point in difpute,
which muft evidently fall to the ground, i f the obfervations made for finding the variation
in Captain Cook’ s voyage are not fufficient to fupport it. What then muft. become
of it, i f M . Bouvet’ s obfervations, o f this kind, were liable to an equal, or a
greater error t which, without any reafonable caufe for offence, we might fuppofe
they were.7 -
It is not neceffary to account for thefe differences in the obferved variations in this
place, nor yet to point out the reafons why fuch anomalies have not been noticed in
observations o f this kind before. I ihall, however, remark, that I have hinted at
fome of the caufes in my introdu&ion to the obiervations which were made in Captain
^ ° °k s ^econ<^ voyage j and many others will readily offer themfelves to perfons who
have had much pra&ice in making thefe obfervations, and who have attentively con-
fidered the principles on which the inftruments are conftrufted, and the manner in which
they are fabricated. Nor is it at all furpriiing, that the errors to which the inftruments
and obfervations o f this kind are liable, ihould not have been difcovered before,
iince no navigators before us ever gave the fame opportunity,> by multiplying their
■obfervations, and making them under fuch a variety o f circumftances as we did.
Haying now fully ihewn, that the circumftances, brought forward by M. Le Mo-
nier, in fupport o f his argument, are neither fuch as can be depended on, nor yet
■■ fairly
„ M S » « “ aie *” ‘he ftc0nd Vo1 1 1 February 2, 1773, p. '3,7.1. March 18,,
Aueuft '18 1- %naat^ t>2^’ r l27$ ’ P' See Obfervations made laft Voyage,
fanuaVv a l . , ■! ¥ ' ,2 ? 7’ a" d ‘ 4’ F' W b and !9°- December 12, p. ibid.
1780, p. S i and May^1*9/ pf 21^^ ^ P‘ 4°9- ‘6‘
Vox; I.