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248 JOURNEY OF MAUPERTUIS;
compute twelve of thefe, and in {pite of fome triangles improper for fuch computations,
from the fmall angles they contained, we found the greateft difference given in the
diftances between Kittis and Torneo did not exceed 54 toifes in the wideft of thefe com-
binations, and we fixed on two which we deemed preferable to the reft, the difference
between which was 4 toifes, the mean of which we took to determine the length of our
arc.
The fmall difference between any of thefe refults would have furprized us if we had not
known how much time and care had been taken in obferving our angles. Eight or nine
triangles had coft us fixty-three days, and every angle had been fo often taken, and by
fo many different obfervers, that the mean of all thefe obfervations could not fail to be
very near the truth.
‘The {mall number of our triangles enabled us to make a fingular calculation, and
which would fhew the fulleft extent of ali the errors which the greateft aukwardnefs
and moft complete misfortune, joined together, could poflibly produce. We placed as
a pofition that in all the triangles from the bafe, we had made an error of 20“ in each of
the two angles, and 407 in the third, and that all thefe errors were on the fame fide, and
tended to diminifh the length of ourarc. And the refult, allowing fo ftrange a pofition,
was that 543 toifes of error was the whole that it could occafion.
The care with which we had meafured the bafe left no apprehenfion on that fcore.
The agreement of a great number of intelligent perfons who feparately wrote the num-
ber of rods; and the repeating of this meafurement, with only four inches of variance,
made a certainty of correétnefs even more than fufficient.
The reft of our examination was therefore turned to the amplitude of our arc, and
the little difference which we found in our obfervations either at Kittis or Torneo left us
nothing to with for of greater nicety.
There feemed, on noticing the folidity and the mode of conftruétion of our fextant,
and the precaution we ufed in tranfporting it, no room to fear that we had any ways
deranged it. ‘The limb, the telefcope, and the centre of this inftrument were of one
piece, the threads in the focus of the object glafs, were of filver, fixed by Mr. Graham
in fuch manner that no change of their pofition could happen, fo that in fpite of the
effects of heat and cold, they remained equally extended. So that the inftrument could
no otherways be out of order than by its figure being altered and the telefcope bent, but
if a computation be made of the effeéts of fuch a change, it will be feen that in order
to caufe an error of a fecond in the amplitude of our arc, it muft be fo much bent as
to be eafily perceived. ‘This inftrument was tranfported from Kittis to Torneo by water
in a very folid box: always fome of us were with it, and on pafling the cataracts it was
carried by men.
Moreover, the pofition of the ftar which we had obferved, fecured us againft any
flexion which one might apprehend could happen either to the radius on the tele-
fcope of thefe large initruments, when the {tar to be obferved fhould be diftant from the
zenith, and the in{trument fhould be inclined to dire&t it to the flar. Their weight
alone might make them bend, and the pra¢tice of obferving a ftar with the two dif.
ferent fides of the inftrument which may remedy other accidents would be of no avail in
this inftance: for if any-flexion fhould take place in the inftrument while obfervin
with its face towards the eaft; on turning it towards the weft there will be a new flexion
in the oppofite direction, and nearly equal; fo that the line which anfwered with the
zenith when the front of the inftrument was turned towards the eaft, will very poflibly
ahfwer the fame when turned towards the weft ; and yet the arc which meafures the
diftance from the zenith be wrong. ‘The diftance of our ftar from the zenith of Kittis
was
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