But if in any system a comet with a tail move near some powerful planet, what will be the consequence? why, the matter emitted from the body of the comet will be attracted round the planet; and by the comet's sending out new matter, or a sufficient quantity being already emitted, there will arise a continual flux of matter round the planet; and though the column, emitted from the comet, may at first be either of a cylindrical, conical, or any other form, yet its centrifugal force, with the gravities arising both from the planet and from the effluent matter, will always render it broader and thinner; and thus a reason might be assigned for Saturn's ring, the most surprising phenomenon in nature.

And while the tail of the comet would furnish the planet with such a ring, the comet itself might probably be attracted, if at a due distance, and become a new satellite to the planet; and thus, probably, several comets have furnished out both Saturn's satellites and his ring; for it is not likely that Saturn's ring is owing to the effluvia of one comet, since it projects a shadow on his disk; whereas the matter of the tails of comets is so rare, that the stars may be seen to shine through it. Saturn's ring, therefore, seems to consist of the talls of several comets, whose matter is become more dense on account of his attraction.

It is evident that a planet may acquire satellites, and yet. not a ring; for all comets have not a tail; and if a comet without a tail be attracted, it will furnish the planet a satellite without a ring.

The great Sir Isaac Newton has concluded, that the vapours of comets are dispersed among the planets; nay, he reckoned this communication necessary, in order to repair the loss of liquid matter. And Dr. Halley and Mr. Whiston are of opinion that both comets and their tails cause considerable changes in the planets, as a variation in their poles, or deluges, and conflagrations; but comets may possibly produce more benign effects, and even sometimes supply the planets with useful and surprising things.

On the Nature of Intermitting and Reciprocating Springs By Mr. JOSEPH ATWELL, F.R.S.-[1732.]

THE following conjectures on the subject of intermitting and reciprocating springs were suggested to Mr. Atwell by the phenomena of a particular fountain he had seen the winter before:

The spring is situated at one end of the town of Brixam, near Torbay, in Devonshire, and is known by the name of Laywell. It is a long mile distant from the sea, on the north and north-east side of a ridge of hills, lying between it and the sea, and making a turn or angle near this spring. It is situated in the side of those hills, near the bottom, and seems to have its course from the south-west towards the north-east. There is a constantly running stream which discharges itself near one corner into a basin, about eight feet in length, and 4 in breadth; the outlet of which is at the farthest end from the entrance of the stream, about three feet wide, and ef a sufficient height. On the outside of the basin are three other springs, which always run, but with streams subject to a like regular increase and decrease with the former. They seem indeed only branches of the former, or rather channels discharging some parts of the constantly running water, which could not empty itself all into the basin; and therefore when, by means of the season, or weather, springs are large and high, on the flux or increase of this fountain, several other little springs are said to break forth, both in the bottom of the basin and without it, which disappear again on the ebb or decrease of the fountain. All the constantly running streams put together, at the time that he saw them, were more than sufficient to drive an overshot mill; and the stream running into the basin might be about half of the whole.

Mr. Atwell made a journey purposely to see it, in company with a friend. When they came to the fountain, they were informed that the spring had flowed and ebbed about 20 times that morning; but had ceased doing so about half an hour before they came. On their return to it, a man, who was still at work near it, said that it began to flow and ebb about half an hour after they went away, and had done so 10 or 12 times. In less than a minute, they saw the stream coming into the basin, and likewise the others on the outside of the basin begin to increase and to flow with great violence; on which the surface of the water in the basin rose an inch and a quarter perpendicularly, in near the space of two minutes: immediately after which, the stream began to abate again to its ordinary course; and in near two minutes' time the surface was sunk down to its usual height, where it remained near two minutes more. It then began to flow again as before; and in the space of 26 minutes flowed and ebbed five times; so that, an increase, decrease, and pause, taken together, were made in about five minutes, or a little more.

Mr. Atwell imagines them to be occasioned by two streams or springs, one of which passing through two caverns or natural reservoirs with syphons, meets with the other stream in a third reservoir, without a syphon; where, being joined, they come out of the earth together.

The supposition of reservoirs and syphons in the bowels of the earth has been made by others. But whoever has seen the Peak of Derbyshire, the hilly parts of Wales, or other countries, must be satisfied that they abound with caverns of many sorts. Some of them are dry, others serve only for passages, or channels to streams, which run through them; and a third sort collect and hold water, till they are full. They must also have observed, that there are sometimes narrow passages, running between the rocks which compose the sides, and going from one cavern to another. Such a passage, of whatever shape or dimensions, how crooked and winding soever in its course, if it be but tight, and runs from the lower part of the cavern, first upwards to a less height than that of the cavern, and then downwards below the mouth of the said passage, will be a natural syphon.

A natural reservoir then, A B C D, with such a natural syphon, MNP, may be supposed. Let a feeding stream enter it, near the top, at O. The cavern must contain all the water which comes in at O, till it is filled to the top of the syphon at N. Then the syphon beginning to play, and being supposed always to discharge more water than comes in by the feed-E ing-stream at O, will empty the cavern,

till the water is sunk in it below the mouth of the syphon at M; when it must stop, till the cavern is filled, and the syphon runs again as before. If the water discharged by such a syphon, MP, be brought out of the earth by a channel, PQ, the water will flow out of the earth, and stop alternately, making an intermitting fountain at Q. By this plain and easy contrivance, several of the flowing and ebbing springs, observed by the naturalists, may probably be explained; and even a much greater variety of them than is hitherto known.

Experiments to prove the Existence of a Fluid in the Nerves.

By Alexander STUART, M.D. F. R.S.— [1732.]

Exper. 1.-DR. STUART suspended a frog by the fore legs in a frame, leaving the inferior parts loose; then the head being cut off with a pair of scissors, he made a slight push perpendicularly downwards, on the uppermost extremity of the medulla spinalis, in the upper vertebra, with the buttonend of the probe, filed flat and smooth for that purpose; by which all the inferior parts were instantaneously brought into the fullest and strongest contraction. This he repeated several times, on the same frog, with equal success; intermitting á few seconds of time between the pushes, which, if repeated too quick, made the contractions much slighter.

Exper. 2.-With the same flat button-end of the probe he pushed slightly towards the brain in the head, on that end of the medulla oblongata appearing in the occipital hole of the skull; on which the eyes were convulsed. This also he repeated several times, on the same head, with the same effect.

Exper. 3. He tied a piece of fine twine, or thread, parallel to the crural artery, vein, and nerve of a dog; and made a ligature on them, and on the parallel twine, above and below, at the distance of about four inches; then he cut beyond the ligatures above and below, so as to take out the vessels and nerve, with the parallel twine, in one bundle; and laying them on a board, both the artery and vein contracted immediately, and were shortened to almost one half of the natural length which they had in the body, viz. to 24 inches; whereas the nerve remained uncontracted, at its natural length, and commensurated to the parallel twine of four inches, as before it was cut out of the body.

By which it appears that the proportion of the bloodvessels in their completest contraction, to the same in a state of extension, and to the nerves at their constant and natural length, is nearly as five to eight; or, which is the same thing, any given section of a blood-vessel, cut out and left to itself, is capable of contracting, so as to lose parts of its length.

The first two experiments show, that the brain and nerves contribute to muscular motion, and that in a very high degree.

The third experiment makes it as plain, that what they contribute in muscular motion cannot arise from, or be owing to, elasticity, which they have not.

What remains, therefore, but to conclude, that the action of

the nerves in muscular motion is owing to the fluid they contain, by whatever name we may choose to call it.

Experiments on the Friction of Pulleys. By the Rev. J. T. DESAGULIERS.[1732.]

THE first experiment was made with a tackle of five brass sheevers in iron frames or blocks; that is, three sheevers in the upper block, and two in the lower. The sheevers were five inches in diameter, the pins half an inch, and the rope three quarters. Having made an equilibrium, by hanging one hundred and a quarter at the lower block, and a quarter of a hundred at the running rope, he added 17 pounds before the power could go down and raise the weight.

Two hundred and a half being balanced by half a hundred, the addition of 28 lb. made the power raise the weight.

In the experiment 174 pounds exceed by 4 pounds the sum of the frictions deduced from the theory. But in the second experiment, 28 pounds exceed the sum of the friction but one pound.

The reason of this appeared to be, that the rope at first was too large for the cheeks that held the sheevers; but in the second experiment, where the rope was more stretched, it was somewhat diminished in diameter, and so brought off from rubbing so hard against the cheeks.

Of a Beaver. By C. MORTIMER, M.D. R.S.S.—[1733.]

In the Memoirs of the Academy of Sciences at Paris, for the year 1704, is an extract of a letter from M. Sarrasin, the king's physician in Canada, concerning the dissection of a beaver. He says, the largest are three or four feet long, and about a foot or 15 inches broad in the chest, and in the haunches; that they commonly weigh about 50lb.; that they usually live to the age of 20 years; but Francus says, they live 30 or 40 years, and that he heard of a tame one being kept 78 years: perhaps the European may generally be longer lived than the American.

Dr. Sarrasin says further, that a great way north these animals are very black, though there are some white ones to be seen; those in Canada are commonly brown; but their colour grows lighter, as they are found in more temperate countries; for they are yellow, and even almost of a strawcolour in the country of the Illinois and Chaovanons.

As to their manner of living; they choose a low level