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XIX. On a Periscopic Camera Obscura and Microscope. By
William Hyde Wollaston, M. D. Sec. R. S.
XX. Further Experiments and Observations on the influence of
the Brain on the generation of Animal Heat. By B. C. Brodie,
Esq. F. R. S. Communicated to the Society for promoting the
knowledge of Animal Chemistry, and by them to the Royal
P. 378

XXI. On the different Structures and Situations of the Solvent Glands in the digestive Organs of Birds, according to the nature of their Food and particular Modes of Life. By Everard Home, Esq. F. R. S. p. 394 XXII. On some Combinations of Phosphorus and Sulphur, and on some other Subjects of Chemical Inquiry. By Sir Humphry Davy, Knt. Sec. R. S. p. 405 Presents received by the Royal Society, from November 1811 to June 1812.

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Of the figures intended to illustrate Mr. PLAYFAIR's paper in the last volume of the Transactions, Fig. 3 is named by mistake Fig. 1. Fig. 1 was omitted by accident, and is to be found at the end of this Part of the Transactions.

Philosophical Transactions, 1811, page 230, line 13, for 8h 35' 45" read 8h 2′ 5′′. Page 151 of this volume of the Transactions, line 20, for half read double.



XII. Observations of a second Comet, with Remarks on its Construction. By William Herschel, LL. D. F. R.S.

Read March 12, 1812.

As we have lately had two comets to observe at the same time, I have called that of which the following observations are given, the second. Its appearance has been so totally different from that of the first, that every particular relating to its construction becomes valuable; and notwithstanding the unfavourable state of the weather at this time of the year, I have been sufficiently successful to obtain a few good views of the phenomena which this comet has afforded.

A short detail of the observations, in the order of their relation to the different cometic appearances, is as follows:

The Body of the Comet.

January 1, 1812. I viewed the second comet with several of my telescopes, and found it to have a considerable nucleus surrounded with very faint chevelure.

Jan. 2. The comet had a large round nucleus within its faint nebulosity. Not seeing it very well defined, and of so H h


large a diameter, I doubted whether it could be the body of the comet; but although it might be called very large when supposed to be of a planetary construction, it was much too small for the condensed light of a head; its diameter, by estimation not exceeding 5 or 6 seconds.

By way of comparing the two comets together I viewed them alternately. The first, within a nebulosity which in the form of a brilliant head was of great extent, had nothing resembling a nucleus: the light of this head was very gradually much brighter up to the very middle; its small planetary body being invisible. The second comet, on the contrary, although surrounded by a faint chevelure, seemed to be all nucleus; for the abrupt transition from the central light to that of the chevelure would not admit of the idea of a gradual condensation of nebulosity, such as I saw in the head of the first comet; but plainly pointed out that the nucleus and its chevelure were two distinct objects.

Jan. 8. The comet had a pretty well defined nucleus with very faint chevelure. When magnified 170 times the nucleus, though less bright, was rather better defined.

Jan. 18. Within a very faint chevelure I saw the nucleus as before.

Jan. 20. The air being uncommonly clear, I saw the body of the comet well defined; and as the moon was already so far advanced in its orbit as to render future opportunities of viewing the comet very improbable, I ascertained the magnitude of its body, with a very distinct 10 feet reflector, by the following three observations.

First with a low power, which gave a bright image of the nucleus, I kept my attention fixed upon its apparent size; then

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