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JOURNEY OF MAUPERTUIS, 241
was the amplitude of the are of the terreftrial meridian between Kittis and Torneo,
This is a fimple operation : it does not even require that one fhould have the pofitive
diftances of the ftar from the zenith of each place ; it is fuflicient to take the difference
between the diftances: but this operation exacts the greate{t nicety and the utmoft pre-
caution. We had for the purpofe a fextant of about nine feet radius, fimilar to that
which Mr. Bradley ufes, and with which which he made his curious difcovery of the
aberration of the fixed ftars. ‘The inftrument was made at London, under the infpec-
tion of Mr. Graham, of the Royal Society of England. ‘This able mechanic had ftu-
died to unite in it every advantage and convenience that we could defire, and himfelf
graduated the limb.
There are too many things to notice in this inftrument for my giving now a complete
defcription of it. Although what properly conftitutes the inftrument be very fimple, its
fize, the number of pieces ferving to render it commodious to the obferver, the weight of
a large pyramid nearly twelve feet high, which forms its pedeftal, made its getting up to
the fummit of the mountains of Lapland almoft an impracticable matter.
On Kittis two obfervatories had been built : in one was the time-piece of Mr. Gra-
ham, a quadrant of two feet, and an inftrument confifting of a telefcope fixed perpen-
dicularly, and moveable about an horizontal axis, for which as well we were indebted
to the care of Mr. Graham : this inftrument was placed exactly in the centre of the
fignal, which ferved as a point to our laft triangle ; it was ufed for determining the di-
rection of the triangles with the meridian. ‘The other obfervatory, much larger, was
adjoining, and fo nigh that one could diftin@lly hear the ticking of the time-piece from
one to the other; the fextant almoft filled it. I fhall fay nothing of the difficulty of
tranfporting fo many inftruments to the top of the mountain : it was effected, the limb of
the fextant was placed exaétly on the level of the meridian we had traced, and we fatisfied
ourfelves of its exactnefs, by the time of the pafling of a ftar of which we had taken the
elevation. ‘To fum up, every thing on the thirtieth of September was ready to begin
obferving, and the fucceeding days the obfervations of the ftar ¢ of the Dragon were
made, in which the greateft difference that occurred did not exceed 3’.
While obferving this {tar with the fextant, the other obfervations were not negledted :
the time-piece was regulated every day with care by correfponding elevations of the fun ;
and with the inftrument which I before mentioned we obferved the paflage of the fun,
and the time of its pafling the verticals of Niemi and Pullingi, By thefe means the
fituation of our heptagon in refpect to the meridian was afcertained, and eight of thefe
obfervations, the difference between the wideft of which did not amount to a minute,
gave for a mean of the angle formed with the meridian of Kittis, by a line drawn from
the fignal of Kittis to the fignal of Pullingi, 28° 51’ 527.
All thefe obfervations were very happily completed, but rains and fogs had fo: much
retarded them, that we had reached a period at which it was f{carcely poflible to under-
take a return to Torneo; neverthelefs other correfponding obfervations upon the fame
{tar remained to be made there, and we were defirous that the {malleft poifible interval
fhould occur between the obfervations, in order to obviate the errors which might arife
from any motion of the ftar (in cafe it fhould have any of which we were ignorant).
It is fufficiently diftinguifhable that the whole of this operation being founded upon
the difference of the meridional height of a certain ftar obfervel at Kittis and at Torneo,
it is neceflary that the ftar fhould maintain the fame pofition; or at lea{t if it fhould be
diable to any change of elevation that it fhould be known, in order not to confound fuch
motion with the curve of the arc defired.
Aftronomers for many ages have noticed a revolution of the flars round the pales of
VOL. I. Vl the
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