1816.] Royal Institute of France. 157 
1,048364. This last in the parabola had been found 0-9609951, 
less of consequence by 0:087367. ‘This is about +, of the great 
semiaxis of the earth’s orbit. The longitude of the node is 
13° 56’ 43” greater than in the parabola. ‘The inclination is also 
greater in the hyperbola, but only 36 minutes. It would have been 
curious to have found at the end of the calculations the comparison 
of the two orbits with the observations. Mechain had made 12, 
and Pingré assures us, that the errors of the parabola did not ex- 
ceed a minute and a half. M.Kramp has only employed three; 
the total interval is only eight days, By another combination the 
interval is reduced to five days. Perhaps so small an are is, not 
sufficient to warrant the conclusion that the orbit is really hyper- 
bolic. But whether parabolic or hyperbolic, we can have no hopes 
of seeing the comet again, and therefore the question will always 
remain undecided. Astronomers will learn with interest. that 
M. Kramp announces a sequel to this third memoir. 
At the last meeting of the year, on the 26th of December, 
M. Desmarets read a Memoir on the Tides in the English Channel. 
From the soundings given in the French Neptune, and the charts: 
of Dr. Halley, the author begins by giving a general plan of the 
basin. He determines the different depths of the waters of the 
sea, both towards the two coasts and in the middle of the channel. 
From these data, from the situation of the coasts of America, and 
the effects of the luni-solar attraction, combined with the general 
motion of the waters of the sea, M. Desmarets derives an expla-_ 
nation of the considerable tides observed on the cozst of Britanny. 
We want room for a more exact analysis, and therefore refer to the 
memoir itself. 
M. Biot at the same meeting presented to the Class new re 
searches on the phenomena and laws of polarisation. 
M. Burckhardt has communicated new calculations respecting the 
comet of 1786. ‘This comet could only be twice observed, which, 
as is well known, is not sufficient for determining its orbit. As a 
substitute for the third observation, M. Burckhardt makes the most 
probable suppositions for the distance of the comet from the earth. 
These different hypotheses conduct him to four orbits, the difference 
between which are sufficiently small .to induce us to hope that the 
comet might be recognised in case it should return. The author 
of this memoir, who has much practice in these ‘calculations, re- 
garded generally as very troublesome, and which he is better able to 
abridge than any other person, endeavours to draw every advantage 
from this facility. He does not wish to allow any thing to be lost, 
and endeavours to supply what is wanting to us. In this view he 
has examined what was the greatest distance which could be sup- 
posed between the earth and the comet. He has found that it 
could not exceed 0,942. In that case indeed the elements would 
undergo-pretty remarkable alterations ; but this extreme case is very 
little probable. His worthy associate M. Buache, entering into his 
views, and seconding him with equal zeal, is consulting the jourml!s 
