the other a plate which gave rings of the same size as the plate of calcareous spar. But when we combine a system of rings produced by a crystal of zircon, with the system produced by calcareous spar, a different effect is produced; and the system, instead of being diminished, is increased, and is equal to that which would have been produced by a thin plate of calcareous spar, whose thickness is equal to the difference of the thicknesses of the plate of calcareous spar employed, and the plate of calcareous spar that would give rings of the same size as those given by the zircon alone. In the section

on crystals with two or more axes of polarization," Dr. Brewster observes that, although M. Biot considered mica as the only mineral possessing the compound structure indicating two axes, he had found the same structure in topaz, nitre, tartrate of potash and soda, sulphate of potash, acetate of lead, and mother-of-pearl, as early as 1813; and he points out the means of deducing the number of axes in crystals from their primitive forms. Dr. Brewster expresses the general law of the tints for crystals with one or more axes in the following manThe tint produced at any point of the sphere by the joint action of two axes is equal to the diagonal of a parallelogram whose sides represent the tints, and whose angle is double the angle formed by the directions in which the forces are exerted.

ner.

The fourth and fifth sections of this paper relate to the resolution and combination of polarizing forces, and the reduction of all crystals to those with two or more axes; and to the polarizing structure of crystals that have the cube, the regular octohedron, and the rhomboidal dodecahedron for their primitive form. The sixth and concluding section describes the artificial imitation of all the classes of doubly refracting crystals, by means of plates of glass; in which the author demonstrates that the polarizing structure depends entirely upon the external form of the plate, and on the mode of aggregation of its particles. When its form is circular, it has only one axis of polarization, which is attractive if the density diminishes towards the centre, and repulsive if it increases towards the centre; but when its form is rectangular or elliptical, it then has two axes of polarization, the strongest of which appears to be attractive, and the weakest repulsive. The elementary spheroid of crystals with double axes may be supposed, says the author, to be formed by elliptical plates bent into spheroidal strata; and the spheroid itself may be constructed by spheroidal strata of glass, it then exhibiting all the complicated phenomena produced by the simultaneous actions of two unequal axes.

On the Parallax of certain fixed Stars. By the Rev. John Brinkley, D.D. F.R.S. and Andrews Professor of Astronomy in the University of Dublin. Read March 5, 1818. [Phil. Trans. 1818, p. 275.]

Since the author's former observations on the parallax of a Lyræ, published by the Royal Society in a Letter to Dr. Maskelyne, he (the author) has met with apparent motions in several of the fixed stars,

which he could only explain by referring them to parallax. Among these stars, a Aquila exhibited the greatest change of place.

In consequence of the Astronomer Royal having doubted the correctness of the author's conclusions upon this point, he has anxiously engaged in observations relating to it during the last sixteen months; and although the results in respect to a Lyra and to Arcturus have not been very uniform, the recent observations on a Cygni are consistent with the former ones, and exhibit the same discordance between the summer and winter observations as before. In regard to a Aquila also, the observations detailed in the present paper are remarkably coincident with those formerly detailed; and the author thinks that it is to this star we must look for the final decision of the question concerning parallax.

Referring to Mr. Pond's observations, Dr. Brinkley is led to entertain doubts of the fitness of an instrument similar to the Greenwich mural circle for so delicate an inquiry, founded upon remarks detailed in the paper respecting the elements used in computing the index error, and which are independent of the uncertainties to which the observation itself is also subject. It is, however, from the uncertainty of the elements used in the reductions, and not from any errors of the observations, or from any defect in the construction of the instrument alluded to, that Dr. Brinkley is induced to consider the observations hitherto made at Greenwich as not affording conclusive results as to the existence or non-existence of parallax. In the present state of astronony, however, it will be allowed that the relative fitness of instruments for ascertaining with precision the smaller motions, whether real or apparent, of the fixed stars, is an object of import

ance.

On the Urinary Organs and Secretions of some of the Amphibia. By John Davy, M.D. F.R.S. Communicated by the Society for the Improvement of Animal Chemistry. Read April 2, 1818. [Phil. Trans. 1818, p. 303.]

In several species of serpents which were examined by Dr. Davy, the kidneys were nearly as large as the liver, long, narrow and lobulated, and without a pelvis. Each lobule sends a small duct to the ureter, which terminates in a papilla situated in the cloaca, between the mouths of the oviducts, and having its point directed towards a receptacle for the urine, which, though a continuation of the intestine, may be considered as distinct from the rectum and cloaca, with which it communicates only by sphincter orifices.

The urinary ducts often contain a white matter, visible through their coats, which gradually accumulates in the receptacle till it forms a mass which, when of so large a size as to distend the part, is usually expelled by an extraordinary effort of the animal, most commonly in the act of devouring its food. The urine, at first soft, gradually hardens by exposure, and then looks like chalk; it consists of nearly pure uric acid.

The author next relates his experiments and observations upon the urine and urinary organs of lizards. He examined four species, -the gecko, iguana, the kobbera-guion, (described by Knox,) and the alligator. The kidneys vary in size; each ureter has a papilla situated in the receptacle; in other respects the structure resembles that of snakes. The secretion is also nearly similar; that of the alligator contains, besides uric acid, carbonate and phosphate of lime; in one case it smelt strongly like musk.

In two species of the testudo, Dr. Davy found the kidneys lobulated like those of the preceding animals. In the bladder both of the turtle and tortoise he found flakes of uric acid in a transparent liquid, containing mucus and common salt, but no urea.

On a Mal-conformation of the Uterine System in Women; and on some Physiological Conclusions to be derived from it. In a Letter to Sir Everard Home, Bart. V.P.R.S. from A. B. Granville, M.D. F.R.S. F.L.S. Physician in ordinary to H. R. H. the Duke of Clarence; Member of the Royal College of Physicians, and Physician-Accoucheur to the Westminster General Dispensary. Read April 16, 1818. [Phil. Trans. 1818, p. 308.]

The uterus described in this paper had acquired its full development upon the right side only. The left side exhibited a straight line, about half an inch distant from its centre. Upon this side also all the appendages of the uterus were deficient, though their rudiments might be traced. This woman was the mother of eleven children of both sexes, and had been delivered of twins, male and female, a few days before her death, which was occasioned by diseased heart and aneurism of the aorta.

Dr. Granville remarks that this is the first case upon record which disproves the opinion that the different sides of the uterus are concerned in the production of the two sexes. It also shows that twins

of both sexes may be derived from one ovarium.

This paper concludes with some remarks upon supposed cases of superfœtation.

New Experiments on some of the Combinations of Phosphorus. By Sir H. Davy, LL.D. F.R.S. V.P.R.I. Read April 9, 1818. [Phil. Trans. 1818, p. 316.]

Since the author's former communication upon the above subject to the Royal Society, various researches have been brought forward, differing in their results from his own as well as from each other. Sir Humphry concluded that the phosphoric acid contained about, three fifths its weight of oxygen, or twice that contained in the phosphorous acid. Berzelius considers the phosphoric acid as composed of 100 phosphorus + 128-17 oxygen; and Dulong, of 100 phosphorus +124-5 oxygen: and both these chemists consider the

oxygen in the phosphorous acid to be to that in the phosphoric as 3 to 5.

After showing that the only possible source of error in his former experiments was the smallness of the quantity of the phosphorus burned, Sir Humphry describes various modes of effectually carrying on the combustion upon a larger scale, and gives the preference to that in which the vapour of phosphorus, passing from the orifice of a small tube, is made to burn in a retort filled with pure oxygen. The mean result of several experiments carefully conducted upon this plan, gave the composition of phosphoric acid at 100 phosphorus + 134.5 oxygen.

The author having shown the insufficiency of Dulong's method for ascertaining the composition of phosphoric acid and of the chlorides of phosphorus, proceeds to detail his researches upon the latter compounds, and upon the constitution of phosphorous acid. The result of several experiments indicated the composition of perchloride of phosphorus to be 100 of phosphorus + 6 of chlorine; and showed that phosphorous acid contained half the quantity of oxygen existing in the phosphoric acid, and the liquid chloride half the quantity of chlorine contained in the solid perchloride. These experiments sufficiently agree with each other to afford the means of determining the equivalent number of phosphorus. Thus, if phosphoric acid be supposed to consist of two proportions of oxygen and one of phosphorus, the number representing the proportion in which phosphorus combines will be 22.3. If the absorption of chlorine in forming phosphorane be made the datum, the number will be 22.2. If the quantity of horn silver formed from the liquid chloride be assumed as the datum, the number will then be 23.5. The mean of all is 22.6, or the double 45.2, from which, if we take away the decimal, we obtain 45. The author's experiments upon phosphate of potash also agree with this number.

The next subject discussed in this paper is the hypophosphorous acid of M. Dulong. Although Sir Humphry has satisfied himself of the existence of this acid, he is not disposed to regard the methods of analysis adopted by its discoverer as satisfactory. When hypophosphite of baryta is decomposed by heat, it is converted into phosphate of baryta and hydrophosphoric gas; and knowing the quantity of acid in the former, and of phosphorus in the latter, it is easy in this way to learn the composition of the hydrophosphorous acid. The results of Sir Humphry's experiments, however, lead to the conclusions adopted by Dulong; namely, that the quantity of oxygen in the hydrophosphorous acid is half that which is contained in the phosphorous acid. M. Dulong has suggested that the acid described by the author as a mixture of phosphorous and phosphoric acids, is a peculiar chemical compound, and proposes to call it phosphatic acid; but as it has no crystalline form, nor any marked characters; as it is not of uniform composition; and as phosphorous and phosphoric acids mixed, produce a substance of the same kind,—Sir Hum

phry does not admit of this conclusion. The author has adopted throughout the calculations in this paper the supposition that the hydrogen in water is as 2 to 15 to the oxygen; and consequently, he says, has taken the number 15 to represent the latter element. If the hypophosphorous acid be regarded as a simple compound of oxygen and phosphorus, it will consist of 45 phosphorus + 15 oxygen; phosphorous acid of 45 phosphorus +30 oxygen; phosphoric acid of 45 phosphorus + 60 oxygen.

Sir Humphry concludes this paper with some incidental observations relating to the compounds of phosphorus.

New Experimental Researches on some of the leading Doctrines of Caloric; particularly on the Relation between the Elasticity, Temperature, and latent Heat of different Vapours; and on Thermometric Admeasurement and Capacity. By Andrew Ure, M.D. Communicated by W. H. Wollaston, M.D. F.R.S. Read April 30, 1818. [Phil. Trans. 1818, p. 338.]

This paper is divided into three sections. In the first the author, after taking an historical view of the different experiments undertaken by Robinson, Watt, Dalton, Biot, and some others, relating to the elastic force of vapours arising from different bodies at different temperatures, and after pointing out the sources of error and imperfection to which they are liable, proceeds to describe the apparatus which he employed, which is further illustrated by an annexed drawing. The space which contains the vapour for experiment is about half an inch of a barometer tube, against which the oblong bulb of a delicate thermometer rests so as to indicate the true temperature. The contrivance is such, that though the liquid and incumbent vapour are restricted to the summit of the tube, its progressive range of elasticity may be measured from 0° to 200° above the boiling point of water, or from an elasticity of 0.07 inch to that capable of sustaining 36 feet of mercury, without heating the mercurial column itself. In this section of the paper are several tables of results, showing the elastic force of the vapour of water in inches of mercury, at temperatures between 24° and 312°; and also that of alcohol, ether, oil of turpentine, and naphtha. The second section of Dr. Ure's paper relates to thermometric admeasurement, and to the doctrine of capacity. He does not consider the thermometer liable to the uncertainties which are supposed to belong to it by Mr. Dalton, but that it is an equable measure of heat, in consequence of its possessing an increasing rate of expansion, and which is compensated for by a quantity of the quicksilver getting out of the bulb into the tube, and consequently out of the action of the heat, the bulb being the only part heated in all ordinary cases.

In the third section, relating to the latent heat of different vapours, Dr. Ure details experiments made to ascertain the caloric existing in different vapours, and the temperatures at which they respectively acquire the same elastic force.