74

Dr. WOLLASTON on a Method, &c.

tion of cold, and the vacuum produced by this condensation gives opportunity for a fresh quantity to arise from the opposite ball, with proportional reduction of its temperature.

According to a theory that does not admit of positive cold, we should represent the heat of the warmer ball to be the agent in this experiment, generating steam as long as there remains any excess of heat to be conveyed. But if we would express the cause of its abstraction, we must say that the cold mixture is the agent, and may observe, in this instance, that its power of freezing is transferred to a distance, by what may be called the negative operation of steam.

The instrument, by which this is effected, may aptly be called a Cryophorus, which correctly expresses its office of frost-bearer.

VIII. A Catalogue of North Polar Distances of some of the principal fixed Stars. By John Pond, Esq. Astronomer Royal, F.R.S.

Read December 17, 1812.

THE catalogue which I have the honour of transmitting to the Society, is the result of a great number of observations made with the new Mural Circle, from the month of June last to the present time.

I hope at no very distant period to add considerably to its precision; but I trust that in its present state, it will not be thought unacceptable to astronomers, as from the experience I have now obtained of the instrument, I may safely pronounce that it far exceeds in accuracy any thing yet known in the history of practical astronomy.

In the fourth column I have annexed the degree of uncertainty, or maximum of error, to which I conceive the results are liable. These numbers not being derived from any strict mathematical process, must only be considered as indicating the opinion I have formed on the subject. When the observations themselves are laid before the Society, I shall have an opportunity of stating at length on what grounds this opinion. was formed..

L 2

76 Mr. POND's Catalogue of North Polar Distances, &c.

a Aquila, a Arietis, and a Ophiuchi are probably determined within a second of the truth, but I have met with some discordances in these stars which I do not come prehend; future observations will shew, whether these are accidental or arise from some periodical cause.

Those stars marked † were determined by the quadrant, its error having been determined by comparison with the circle, by other stars having nearly the same declination.

IX. A Description of the solvent Glands and Gizzards of the Ardea Argala, the Casuarius Emu, and the long-legged Casowary from New South Wales. By Sir Everard Home, BartF.R.S.

Read December 17, 1812.

HAVING, upon a former occasion, laid before the Society an

account of several varieties in the structure of the solvent glands and gizzards of birds, I now avail myself of some further materials, which I have procured since that time, to render the series more complete. The Ardea Argala, a native of Bengal, which feeds upon carrion, and is exceedingly voracious, has the solvent glands differently formed from those of any bird which I have examined; each gland is made up of five or six cells, and these open into one common excretory duct. The glands are disposed in two circular masses, one on the anterior, the other on the posterior surface of the cardiac cavity, putting on a similar appearance to those of the cormorant, but differing both in structure and situation. The gizzard of the Ardea Argala is lined with a horny cuticle, nearly of the same general appearance as that of the crow, and the digastric muscle is of similar strength. These parts are represented in the annexed drawing. (See Plate III.) This bird has a large bag hanging down on the forepart of the neck, which is rendered conspicuous by the skin that covers it being almost entirely without feathers, having only a few scattered on the most prominent depending part. The bag appears to

78 Sir E. HOME's Description of the solvent Glands, &c.

be readily filled and emptied at the will of the bird: upon examination after death, this bag was found to contain air, and tó be unconnected with the organs of digestion, or the trachea which passes down along the middle of its cavity; it communicates by a large oval aperture with the air cells on the posterior part of the neck, and through them receives air from the lungs. The two species of casowary, Casuarius Emu, and the long-legged casowary from New South Wales, differ from one another in the form of their digestive organs, as well as in the length of their intestines.

In the Casuarius Emu, the solvent glands are oval bags one fourth of an inch long and only one-sixteenth of an inch wide; they occupy the whole surface of the cardiac cavity which is very large, and they are all placed nearly in a transverse direction respecting the cavity, the orifices of the excretory duct appearing very distinctly through the membrane which lines the cardiac cavity. The gizzard is nearly of the strength of that of the crow, but has a thicker cuticular lining. This cuticle extends beyond the cavity of the gizzard both above its orifice and downwards towards the duodenum. The most remarkable circumstance respecting the gizzard, is its being situated out of the direction of the cardiac cavity, forming a pouch on the posterior part, and having before it an open channel lined with cuticle, along which the food can readily pass into the duodenum without being received into the gizzard, as in other birds. At the commencement of the duodenum there is a broad valve, upon the edge of which the cuticular lining of the cavity of the gizzard terminates. The duodenum, at its origin, swells out into an oval cavity four inches long, and two and an half in diameter; it then contracts to one inch and a half in dia