1807.] 
committed in 1736, M. de Lalande endea- 
voured, from his long experience, to point 
Out the way that might lead to the desired 
explanation. He has suggested, that, at 
this period, they were wholly ignorant of 
the use of the proof-telescope. This in- 
strument is so convenient and simple, 
that we might be induced to believe its 
hivention to be nearly of the same date 
as the application of sights to sextants 
and-quadrants; it 1s however more mo- 
dern than might be supposed, and is ge- 
nerally employed without our inquiring, 
as is too often the case, to whom we are 
indebted for the discovery. It is men- 
tioned for the first time in De Lalande’s 
Astronomy, edition of 1764. In order 
to verify the parallelism of telescopes, 
Bouguer recommends the employment of 
two sights, which ought to be made reci- 
procally to change’ places, with the view 
of ascertaining if they are of the same 
height. He himself employed a mach 
more imperfect method, and one which 
could still less bear a compartson with the 
proof-telescope of M. De Lalande, which 
is now universally adopted. M. Delam- 
bre professes himself ignorant, whether 
Graham might not employ similar means 
to verify his sextant; Maupertuis makes 
no meution of it in the chapter in which 
he treats of the verification of this in- 
strument, and from this negligence may 
be partly explained the error imputed to 
him. 
This measurement of a degree in Lap- 
land, has furnished M. De Lalande with 
the subject of a second memorr, ir which 
he demonstrates the necessity of attend- 
ing to the level in taking observations at 
a.great distance! | 
The eclipse of the 16th of June last 
created great interest among the astrono- 
mers of Paris; it was, however, one of 
the senior members of the class, M. 
Messier, who alone succeeded in observ- 
ing it. The clouds parted for a moment, 
and permitted him to view its commence- 
ment, which he observed at 4h. 52’ 43”. 
He was also enabled to measure three 
phases, for the accuracy of which, how- 
ever, he does not pledge himself. 
The atmospheric variations, which pre-- 
vented us observing the eclipse, likewise 
proved unfavourable to the observation 
of the solstice, but as this could be sup- 
plied by the observations of the preceding 
and following days, a sufficient number of 
observations has been collected to con- 
firm those made during the last ten years. 
M. Bouvard, who is worthy to be 
yanked with RIM. Messier and Mechain, 
Proceedings of Learned Societies 
173. 
has, we are informed, discovered two co~ 
mets, and calculated their elements, 
The same caiculations have been made 
by Biot and Arago, according to the me- 
thed of Laplace. M. Legendre: failed 
not to embrace this opportunity of verify= 
ing-the formule, which he published last 
year. We then observed, that there are 
fewmethods which nought not prove in= 
convenient, and somewhat inaccurate, 
under certain circumstances, .This has 
in fact been the case in the present in- 
stance. But M,. Legendre has found in 
his analyses sufficient resources to obviate 
the dithculty, which had not been fore= 
seen in his first Memoir, and to simplify 
the veneral solution that he had giver of 
the problem. M. Legendre has, besides, 
been occupied with a more important 
question, though its applications be. less 
common; this memoir is entitled: Anae - 
lyse des triangles traces sur le Spheroide. 
The first astronomers, who measured 
the earth with any degree of accuracy, 
considered it as a sphere, of which the 
radius is of an immense. magnitude, in 
comparison with the smail iitervals which 
they proposed to estimate. he longest 
side of the triangle which entered smto 
these operations did not exceed 60,000 
metres, and the difference of a similar 
arc to the right line joiming its extremi- 
ties was scarcely two decimetres, or one 
three hundred miiliontl part. It was be= 
lieved then with some reason, that we 
might consider as right lines the trie 
angles of which the curve was so little 
evident. 
In the latter operations, when the obe 
ject was to determine more exacily the 
difference between our globe, and a per=. 
fect sphere, they carried their attention 
much farther., The triangles formed on 
the surface of the earth were considered 
as very small portions of a sphere which, 
thronghout the extent of each triangle, was. 
sensibly confounded with the spheroid. 
Does this supposition, which is more ac- 
curate than the former, adimit of all the 
precision that might be expected; and 
since it 1s a spheroid which is to be mea- 
sured, wherefore’have not the triangles 
been estimated as if they were spheroidi- 
cal? This question, says M, Deiambre, 
is so natural, that it must have presented 
itself at once to the astronomers employed 
in this operation, and to the numerous lis 
terati, throughout Ferope, who examin= 
ed and judged respecting the mert of 
their labours. In the first meeting of the 
commission, a learned foreigner; M. 
Tralles, remarked that the bases of Me- 
laa 
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