ther by ligament, and forming a tube communicating from one extremity of the spine to the other.

This species of intervertebral joint, which thus appears common to the fish tribe, is not found to obtain in the whales, as their structure in this, as in many other respects, is the same as that of quadrupeds, but is more distinctly visible, from the vast size of the parts. In them the intervertebral substance is arranged in concentric circles, connected by transverse fibres, the external layers being very firm and compact; but the interior become successively softer, till in the centre there is a soft pliant substance, more like jelly than an organized body, corresponding in its use to the incompressible fluid in fish.

In the bullock, sheep, deer, monkey, and man, the structure corresponds with that of the whale; but in the hog and rabbit a cavity was observed, with a smooth internal surface extending through half the diameter of the vertebræ; so that the structure in these animals imitates that of fishes, though not for any obvious purpose.

In the alligator the several joints are regularly articulated with capsular ligaments, and are lubricated with synovia. In the snake there is a regular ball and socket joint between every two vertebræ ; so that the means employed for the motion of the back-bone in different animals, comprehends almost every species of joint.

Mr. Home's paper has annexed to it an appendix, by Mr. William Brande, giving an account of the chemical analysis of the fluid contained in the intervertebral cavity of the Squalus maximus.

Its specific gravity was found to be 1027. It was not coagulated by heat.

No precipitation was occasioned by infusion of galls, or of catechu; nor was any change produced by alcohol.

But oxymuriate of mercury, muriate of tin, nitrate of silver, and acetate of lead, threw down copious precipitates.

From the effect of these re-agents, it appears to Mr. Brande, that the fluid contains neither gelatine nor albumen; but when the fluid was evaporated to half its bulk, pellicles began to form on the surface, indicating the presence of a variety of animal matter, which the author considers as mucus or mucilage, but which, under certain circumstances of evaporation, is capable of being converted into a modification of gelatine or albumen.

On Platina and native Palladium from Brazil. By William Hyde Wollaston, M.D. Sec. R.S. Read March 22, 1809. [Phil. Trans. 1809, p. 189.]

Until a portion of platina was lately discovered by M. Vauquelin, in some silver ores from Estremadura, the whole of the platina known in Europe was derived from the Spanish possessions in South America, and had very uniformly the same appearance, differing solely in the magnitude of the grains.

A third variety having lately been received from Brazil, the author

thought it deserved particular examination, although the quantity which he could obtain was too small for accurate analysis.

The appearance of this mineral is whiter than Peruvian platina; the grains are rougher and more angular, being evidently fragments of larger masses, very little worn at their surfaces. When examined by solution and precipitation, the greatest part of the grains appeared to be platina nearly pure, as they are free from iron, which forms a considerable part of the Peruvian ore; and apparently free from the several metals, which have within these few years been discovered in that mineral; but they contain, on the contrary, a small quantity of gold, which is not contained in the grains of Peruvian platina.

The author discovered also, among the grains of native platina, a few fragments of native palladium, which he describes as resembling, in the whiteness of their colour, the grains of platina, but differing from them in presenting an appearance of fibres diverging from one extremity. These grains are readily detected by their solubility, and by the red colour of the solution: that they consisted of palladium, was proved by precipitation with prussiate of mercury, or green sulphate of iron, as well as by their fusibility by assistance of sulphur. It is remarked, however, that these grains are not absolutely pure, but contain a very small quantity of platina, which, by its redness when precipitated, seems to be contaminated by iridium.

On a native Arseniate of Lead. By the Rev. William Gregor. Communicated by Charles Hatchett, Esq. F.R.S. Read April 13, 1809. [Phil. Trans. 1809, p. 195.]

The mineral of which this account is given was raised in a very rich copper-mine called Huel-Unity, in the parish of Gwennap, having been found at the depth of fifty fathoms, at the junction of two small lodes or veins. This ore is mixed with some native copper, very rich gray copper, and black copper ore.

It crystallizes in the form of a hexahedral prism, terminated in general by a plane, but sometimes by a taper six-sided pyramid. The colour is generally a shade of yellow, but sometimes wineyellow, like the Brazilian topaz, and sometimes as dark as brown sugar-candy. The hardness varies, and is sometimes sufficient to scratch flint-glass. The specific gravity at 50° temperature is 6:41. Being exposed to heat upon a gold spoon, it melts into a brownishyellow mass, and remains unaltered in a state of ignition. But if heated upon charcoal, it is rapidly decomposed, arsenical vapours being extricated, while the lead is reduced to its metallic state.

The mode of analysis adopted by the author consisted in reducing the ore to a fine powder, and decomposing it by a solution of pure potash, with due precaution to avoid the solution of lead by the alkali along with the arsenic acid. The arseniate of potash was decomposed by nitrate of lead, which gave an arseniate of lead, consisting of known proportions, from which the quantity of arsenic acid in the ore was found to be 26 4 per cent.

The oxide of lead, which had been deprived of its arsenic acid by the potash, was then dissolved in nitric acid, and precipitated by sulphate of soda in the state of sulphate of lead, from which the quantity of lead in the ore proved to be 693 per cent.

Mr. Gregor has found only one specimen in which the proportion of lead to the acid was materially different. In this instance the oxide of lead was 71.45, and the acid 23.88, instead of being, as before, 694 and 26.

Beside these ingredients, the ore also contains a portion of muriatic acid; and the author has also detected small but variable proportions of iron and silica.

The quantity of muriatic acid was ascertained by solution of the ore in nitric acid, and precipitation as usual by nitrate of silver. But Mr. Gregor found it necessary to take certain precautions; for if the solution be made with much heat, part of the muriatic acid is lost by boiling; and if the solution be too concentrated, an arseniate of silver is precipitated along with the muriate, and will then require to be separated, either by solution of it in nitric acid, or by means of its insolubility in pure ammonia, which dissolves the muriate.

In order to determine decisively the nature of the principal acid present in this ore, Mr. Gregor decomposed a portion by sulphuric acid, and, after evaporation of the fluid poured off, reduced a part of the acid upon charcoal. Part was dissolved in water, and precipitated titanium from sulphate of titanium; part was neutralized with soda, and occasioned a brick-coloured precipitate from nitrate of silver, and a reddish yellow precipitate from nitrate of mercury.

From the whole of the experiments detailed in the paper, the author concludes that 100 parts of the ore contain 69·76 oxide of lead, 26.40 arsenic acid, 1.58 muriatic acid; and that the silica and oxide of iron are not essential to its composition.

An anatomical Account of the Squalus maximus (of Linnæus), which in the Structure of its Stomach forms an intermediate Link in the Gradation of Animals between the Whale Tribe and Cartilaginous Fishes. By Everard Home, Esq. F.R.S. Read May 11, 1809. [Phil. Trans. 1809, p. 206.]

The fish described in this account was caught in a herring-net at Hastings, from whence such parts as were more particularly deserving of notice were brought to London for further examination.

It was a male, thirty feet six inches long, and nine feet broad, from the tip of the dorsal fin to the middle line of the belly.

The skin was of a light slate-colour, and though as rough as a new file in the direction from the tail to the head, yet as smooth as satin in the opposite direction.

The mouth was about five feet wide, with six rows in each jaw of small conical teeth, rather curved inwards.

The nostrils were placed on the edge of the upper lip.

The eyes very small, with pupils perfectly round.

Half way between the eye and the gills was an orifice and canal leading to the mouth. The gills five in number on each side.

The fins, and also their situation, are particularly described. Adjacent to the anal fins are placed two holders for the purpose of grasping the female, terminated by a flat, sharp, bony process five inches long, which moves on a joint, and is, in fact, the termination of a series of parts corresponding to the pelvis, femur, tibia, and foot of quadrupeds.

The pectoral fins also correspond in some measure to the anterior extremities, and are connected by cartilages, which answer the same purposes as the scapulæ and sternum of quadrupeds.

The heart was not larger than that of a bullock, with three valves at the origin of the pulmonary artery, three at the entrance of the aorta, and also two sets more, of three each, in the course of the artery, at a short distance from each other.

The stomach contained several pails full of pebbles, a quantity of mucus, and a small portion of substance that looked like the spawn of the oyster.

Beside the cardiac and pyloric portions of the stomach observable in other sharks, there was a globular cavity communicating with the pyloric portion by a very small orifice, and by. another, equally small, with the intestine.

The liver of this fish yielded about three hogsheads of oil. The vessels of the liver were large enough to admit a man's arm. The bile is conveyed direct to the intestine by twelve hepatic ducts, for there is no gall-bladder.

Although the Squalus here described resembles, in many respects, the tribe of Sharks, it is observed to differ essentially in the form of its stomach, which is intermediate between that of the shark and whale.

In the modes of generation, also, as well as in the stomachs, a series of gradations may be observed from whales through the squalus, sharks, rays, and skates, to the proper fishes; but this inquiry will form the subject of a future communication.

Mr. Home closes the present account by such particulars as he could collect concerning a large fish thrown ashore on one of the Orkneys, and described as a sea-snake by those who had seen it half putrid and half devoured by sea-fowl; but it was ascertained by Mr. Home to be in reality another specimen of the same Squalus as that above described.

On an Improvement in the Manner of dividing astronomical Instruments. By Henry Cavendish, Esq. F.R.S. Read May 18, 1809. [Phil. Trans. 1809, p. 221.]

The use of the common beam-compass for dividing having been justly objected to, on account of the danger of bruising the divisions which have been made, by replacing the points of the compass into

them, the author proposes a means of obviating that inconvenience, by substituting a microscope instead of one of the points; and he describes a method of proceeding, in which there is no need ever to set the other point into any division already made.

The beam to be employed for this purpose must have a fixed point at one extremity, and at the other a centre of motion, round which the length of the beam may revolve as radius. A microscope is to slide in a groove along the middle to any required distance from the point; and in order that these may both be over the circle at the same time, the centre of motion must be capable of adjustment, that it may be fixed at a greater or less distance from the centre of the circle, according to the magnitude of the arc intercepted between the point and microscope.

In dividing by continual bisection, the microscope is first to be removed from the point to a distance nearly equal to the chord of the half-arc; and when the centre of motion has been duly adjusted, and the wire of the microscope is made to bisect the dot at one extremity, a faint scratch must be made with the point.

The beam having next been turned half round, and the dot at the other extremity brought under the wire of the microscope, a second scratch is made with the point, which, if the distance has been taken, will be very near the former; and the wire of the microscope will easily be placed midway between them in the further process of bisection, which is again performed in the same manner, after the position of the microscope and of the centre of motion have been duly altered.

In laying down the real divisions from the marks thus made, the centre of motion must be so placed that the whole length of the beam may become a tangent to the circle; and when the microscope has been fixed close to the point, and the first dot brought under it, the first division is to be marked, and the rest in succession till all are made.

Since the entire arc of a circle cannot be divided to degrees without trisection and quinquesection, Mr. Cavendish describes three methods of quinquesection. which it would be difficult to render intelligible without reference to the figures which accompany his paper; and he also makes an estimate of the comparative accuracy attainable in bisection, trisection, and quinquesection.

As it would be difficult to place the centre of motion accurately, so that the point and axis of the microscope shall both be in the circle in which the divisions are made, it becomes necessary that the wire of the microscope should be placed truly at right angles to the length of the beam; for then, although the point of intersection of the circle with the wire of the microscope is not accurately in the middle of the wire, still, when the beam is reversed, the point of intersection will lie at an equal distance on the opposite side of the centre, and will consequently be at a given distance from the fixed point of the compass.