This year exhibiting little else but scenes of confusion and distress
amidst the calamities of an unhappy war, scarce any attention was paid,
by the members of the American Philosophical Society, to astronomical or
any other literary subjects. It was agreed, however, by Mr. Rittenhouse,
Mr. Lukens and myself, to look out whether Mercury would touch the Sun’s
disc the 2d of November this year; as a very small difference of
latitude from what the Tables give, would have carried the planet clear
of the Sun: but, from our observation of the transit of this planet, in
1769, we had reason to expect it would pass further on the Sun, than
Halley’s Catalogue gives it.
The following were the observations made, viz.
Nov. 2d, 1776. I got ready the two f. reflector with the largest
object-glass, and shortest eye-tube, magnifying about 95 times.
At 4^h per clock—No appearance of the planet on the Sun, and did not
expect it until about half an hour past 4; but as Mr. Lukens and Mr.
Rittenhouse had not yet come to me in the college, I sent to hasten
them.
At 4^h 5′ per clock—took my eye from the tube to adjust it, and fix the
smoked glass, to give clearer vision, the atmosphere being hazy. Having
fixed the smoked glass in the proper place, so as to prevent its sliding
or falling with its own weight, and before I had applied my eye to the
telescope again, Mr. Rittenhouse came in; and I desired him to see if
the focus and dark glass were all suitable to his eye, as they were to
mine. I had been about 4′ employed in this adjustment.
At 4^h 9′, Mr. Rittenhouse having put his eye to the tube, immediately
called out, that he saw the planet on the Sun.
At 4^h 10′ per clock, we judged ☿ had entered one-third of his diameter
on the Sun.
At 4^h 17′, we clearly noted the internal contact of the limbs.
At 4^h 45′, we judged the least distance of the nearest limbs to be
rather more than one diameter of ☿; or that the distance of the limbs
was 10″. We-did not apply the micrometer to make any measures; as we
presumed that we could judge the distance as accurately by the eye, as
it could be measured; on account of the haziness of the atmosphere and
the small altitude of the Sun. We kept viewing the planet till sun-set,
the distance of the limbs continuing so nearly the same, that we could
scarce perceive any diminution thereof; though we were sure also, that
it did increase above 10″.[A47]
-----
Footnote A47:
In a table (in the 2d vol. of Lalande’s _Astronomie_,) entitled,
“_Passages de Mercure sur le Soleil, calculés pour trois siècles par
les nouvelles Tables_,” the transit of that planet, above referred to,
is thus set down by Lalande, at Paris; viz.
Year. Conjunct. Mean Geocentric Mid. Mean Semi-dura. Short.
Time. Long. Time dist.
1776. Nov. 2. 9^h10′7″. 7.11°3′36″. 9^h49′53″. 0^h36′42″. 15′43″.A