al announcement of his discovery as given in the
Philosophical Transactions for 1781.

PHILOSOPHICAL TRANSACTIONS, 1781

XXXII.--ACCOUNT OF A COMET

BY MR. HERSCHEL, F.R.S.

(Communicated by Dr. Watson, jun., of Bath, F.R.S.)

_Read April 26, 1781_

[Sidenote: Original announcement.]

"On Tuesday the 13th of March, between ten and eleven in the evening,
while I was examining the small stars in the neighbourhood of H
Geminorum, I perceived one that appeared visibly larger than the
rest; being struck with its uncommon magnitude, I compared it to H
Geminorum and the small star in the quartile between Auriga and
Gemini, and finding it to be so much larger than either of them,
suspected it to be a comet.

"I was then engaged in a series of observations on the parallax of
the fixed stars, which I hope soon to have the honour of laying
before the Royal Society; and those observations requiring very high
powers, I had ready at hand the several magnifiers of 227, 460, 932,
1536, 2010, &c., all which I have successfully used upon that
occasion. The power I had on when I first saw the comet was 227. From
experience I knew that the diameters of the fixed stars are not
proportionally magnified with higher powers as the planets are;
therefore I now put on the powers of 460 and 932, and found the
diameter of the comet increased in proportion to the power, as it
ought to be, on a supposition of its not being a fixed star, while
the diameters of the stars to which I compared it were not increased
in the same ratio. Moreover, the comet being magnified much beyond
what its light would admit of, appeared hazy and ill-defined with
these great powers, while the stars preserved that lustre and
distinctness which from many thousand observations I knew they would
retain. The sequel has shown that my surmises were well founded, this
proving to be the Comet we have lately observed.

"I have reduced all my observations upon this comet to the following
tables. The first contains the measures of the gradual increase of
the comet's diameter. The micrometers I used, when every circumstance
is favourable, will measure extremely small angles, such as do not
exceed a few seconds, true to 6, 8, or 10 thirds at most; and in the
worst situations true to 20 or 30 thi