the fire. Small boards are to be placed, one on the other, for the stand to rest on, until the desired elevation is acquired."

When a workman has got his fire at a temperature that suits his business, and is desirous of registering, by means of a gauge, the amount of heat, that he may be able to acquire it again on other occasions, he is at first to ascertain the mean temperature of the room, which may be sixty-five; he is then to place the cone at the standard distance of two feet opposite the fire, and to count the number of degrees the radiant heat of the fire raises the thermometer above sixty-five. On any future occasion, when the mean temperature of the apartment is sixty-five, he has only to place the cone as before, at the distance of two feet; and when the thermometer is raised the same number of degrees above sixty-five, as in the former experiment; the advantageous degree of heat required, is obtained. When, from the state of the weather, the mean temperature of the apartment varies, an allowance must be made for the difference. This gauge is not complicated, and is not very liable to get out of order.

In using it as a pyrometer to measure the heat of a fire as compared with a thermometer, let us suppose the mean temperature of the apartment, sixty-five; the cone, upon being used to point out the heat of a brisk fire, is placed at the standard distance of two feet, opposite a plate of iron, red hot; the thermometer will be raised above sixty-five, but will be below the degree that marked a brisk fire. If the plate of hot iron be allowed to cool, until its redness is only visible in the dark, the thermometer will indicate less heat, but greater than that of the mean temperature of the apartment. In like manner, if, at the distance of two feet, we present the side of a vessel containing boiling mercury, opposite the base of the cone, the heat indicated will be less than that caused in the last experiment. If, instead of the mercury, we now present, at the same distance, the side of a vessel containing boiling oil, the heat will be less; and a vessel containing boiling water, will cause a still lower indication by the thermometer; but yet the heat will be greater than that of the room. The excess of heat above sixty-five, is to be carefully marked after each experiment.

Thus the pyrometer is founded on the principle, that the radiant heat emanating from a hot body, will raise the thermometer, placed at a fixed distance, above the mean temperature of the room, in proportion as the body is heated; and that, as it cools, the thermometer will fall in the same relative proportion: and that the number of degrees above the mean temperature of the room, will point out the relative degrees of heat of the hot bodies subjected to experiment.

We know the heat of boiling water, as compared with the heat of boiling oil; and we know the comparative heat of boiling oil, to the heat of boiling mercury. When vessels containing mercury or oil, in a state of ebullition, are placed successively at the distance of two feet opposite the base of the cone, their relative effects on the thermometer are to be carefully marked.

In this way, we may compare the effects on the thermometer, pro

duced by a plate of red hot iron, with the effects produced by the side of a vessel containing boiling oil or boiling mercury, and may deduce what its comparative heat is, in reference to the heat of these boiling liquids.

Surfaces of different kinds, differ in their power of radiating heat; therefore, the vessels containing the hot liquids, should be of the same kind; and the sides of the vessels, presented to the base of the cone, should be uniform in colour, and in every other respect. The hot body subjected to experiment, should be larger than the area of the base of the cone.

The great difference between experiments made with pyrometers subjected to the direct action of the fire, encourages attempts to arrive at truth, by a different road. Mr. Prinsep makes the melting point of pure silver, four hundred degrees below the determination of Mr. Daniel. The most sanguine in using pyrometers, expect only to approximate towards the real degree of heat.

What the workman is anxious for, is to keep up a steady heat that suits his business, and he will look with a friendly eye on any self-regulating apparatus, that will keep the heat of his fire from rising above, or falling below, a certain point. In a late number of the Technological Repository, you have given the French plan for regulating the temperature of apartments; the regulator of the fire is very ingenious; but a more delicate regulator suggests itself, in the form of an air thermometer, on a very large scale. Air, heated, expands equally; therefore, if we enclose a portion of air or gas, at a certain distance from the furnace, it will expand as the furnace is heated.

A very large air thermometer is to be made of copper; the copper bulb is to be fastened at a fixed distance from the fire; a large tube, in the form of the letter L, contains the water, which confines the air in the bulb. On the water in the tube, is a float; this float is connected, by means of a wire, with the end of a lever; the wire rises through a stuffing box at the top of the tube. The other end of the lever is connected by a rod, to the register door of the furnace. The register door turns on a horizontal axis, and is easily moved. The lever, by means of grains of shot, for which there is a receptacle provided, is kept in the horizontal position when the heat of the furnace is at the desired point. If the heat should increase, the air in the bulb expands, and the water rises in the tube; consequently, the float rises, and the opposite end of the lever descends, and shuts the register door.

If, on the contrary, the heat should decrease too much, the air in the bulb contracts, the float descends and pulls down the lever, and, consequently, opens the register door.

By regulating the heat of water circulating in tubes, the temperature of hot-houses and apartments may be kept steady for all useful purposes. You have already suggested, in a late number, a very useful application of the French plan for regulating the heat of apartments; namely, to the rearing of silk-worms in England. I am, sir, your obedient servant,

To T. GILL, Esq.

J. M'SWEENY.

Remarks by the Editor.-We have no doubt that some good prac tical results may be obtained by adopting the suggestions of our worthy correspondent. Possibly a polished concave speculum, which would collect and concentrate the heated rays upon the bulb of the thermometer, might be preferable to the cone. [Tech. Rep.

Experiments on the Pressure of the Sea, at considerable Depths. By JACOB GREEN, M. D. Professor of Chemistry, in Jefferson Medical College, Philadelphia.

of re

AMONG the various expedients resorted to for the purpose lieving the tedium and monotony of a sea-voyage, no one is more common during a calm, than to attach to a long line (the log) an empty bottle, well corked, and then to sink it many fathoms in the sea. In all such experiments it is well known, that the bottles, upon being drawn up, are either full, or are partially filled with water. The manner in which the water gets into the bottle, is, in some instances, perfectly obvious, but in others very perplexing, if not wholly inexplicable. Sometimes the cork, however well secured and sealed, is driven into the bottle, and, when drawn up, the vessel is of course, found filled with water; and in such cases, what is a little surprising, the cork is often found occupying its original position in the neck of the vessel, being forced there, no doubt, by the expansion of the dense sea-water, on being drawn near the surface. This seems to be proved by the cork being often in an inverted position. In the above experiment, and in some others to be mentioned presently, the bottle appears to be filled instantly; as the person who lowers the bottle, often feels a sudden increase of weight, somewhat similar to the sensation produced, when a fish takes the hook on a dipsey line.

Sometimes the above experiment is varied, by filling a vessel with fresh water, which, on examination, is found to be replaced by salt water; the cork remaining, apparently, undisturbed.

Sometimes, when the previously empty bottle is only half full of water, this, when poured into a tumbler, effervesces like water highly charged with carbonic acid gas. This is readily explained: for when the bottle descends, it is full of air, and when the water enters, it will, of course, absorb the air; especially when the dense water itself expands as it is drawn towards the surface.

Sometimes the experiment is performed by first corking the bottle tight, and then tying over the cork a number of layers of linen dipped in a warm mixture of tar and wax; in fact, every device seems to have been tried to prevent the entrance of the water by the cork. In many of these cases, when the bottle is drawn up from a depth of 200 or 300 fathoms, it is found filled, or nearly filled with water, the cork sound, and in its first situation, and the wax and tar unbroken. Two experiments are mentioned, in which ves

sels with air-tight glass stoppers were used. In one case, the bottle was broken, and in the other, some drops of water were found in it. How does the water find its way into the bottles? There are two opinions: one is, that it passes through the cork and all its coverings, in consequence of the vast pressure of superincumbent water, in the same manner as blocks of wood are penetrated by mercury, in the pneumatic experiment of the mercurial shower. The other, and less popular opinion, is, that the water is forced through the pores of the glass.

The following experiment, which I made on the 7th of May, 1828, in latitude 48+ longitude 24° 34', will, perhaps, throw some light on this subject.-Mr. Charles Dixey, the obliging and intelligent master of the packet-ship Algonquin, had a boat rowed off from the ship, for me, to the distance of about half a mile, when the sea was almost perfectly calm. A hollow glass globe hermetically sealed, which I had previously prepared in Philadelphia, was then fastened to a line, and sunk, with a heavy mass of lead, to the depth of 230 fathoms, or 1380 feet. On the same line, and 30 fathoms above the glass globe, was fastened a small bottle with an air-tight glass stopper; 50 fathoms above this, a stout glass bottle with a long neck, was tied; a good cork was previously driven into the mouth of this bottle, which was then sealed over with pitch, and a piece of linen dipped in melted pitch, was placed over this; and when cool, another piece of linen treated in the same way, was fastened over the first. Twenty fathoms above this bottle, another was attached to the line, much stouter, and corked and sealed like the first, except that it had but one covering of pitched sail-cloth. Thirty fathoms above this, was a small thin bottle filled with fresh water, closely corked; and 20 fathoms from this last, there was a thin empty bottle corked tight and sealed, a sail-needle being passed through-andthrough the cork, so as to project on either side of the neck.

Upon drawing in the line, thus furnished with its vessels, and which appeared to have sunk in a perpendicular direction, the following was the result:

The empty bottle with the sail-needle through the cork, and which came up the first, was about half full of water, and the cork, and sealing, as perfect as when it first entered the sea.

The cork of the second bottle, which had been previously filled with fresh water, was loosened, and a little raised, and the water was brackish.

The third bottle, which was sealed and covered with a single piece of sail-cloth, came up empty, and in all respects as it descended. The fourth bottle, with a long neck, and the cork of which was secured with two layers of linen, was crushed to pieces, all except that part of the neck round which the line was tied; the neck of the bottle both above and below the place where the line was fastened, had disappeared, and the intermediate portion remained embraced by the line. This I thought a little remarkable; but, perhaps, it may be explained by supposing that the bottle was first filled by the superincumbent pressure, with dense sea-water, which expanded on being VOL. VII.-No. 1.-JANUARY, 1829.

3

drawn up near the surface. Had the vessel been broken by external pressure, that part surrounded with the line, ought to have been crushed with the rest.

The fifth bottle, which had been made for the purpose of containing French perfumery, or æther, and which was, therefore, furnished with a long close glass stopper, came up about one-fourth filled with

water.

The hollow glass globe, hermetically sealed, which was the last, and had been sunk the deepest of all, was found perfectly empty, not having suffered the smallest change. It is, therefore, concluded, that at the depth of 230 fathoms, the water enters glass vessels through the stoppers and coverings which surround them, and not through the pores of the glass. What the effect of a pressure of 400 fathoms or more will have on the glass globe above-mentioned, Captain Dixey has engaged to ascertain for me on his return to America, if opportunity shall offer.

[Phil. Mag.

Account of a new method of projecting Shot, discovered by
MR. SIEVIEre.

Ar a meeting at the Royal Institution in London, held on the 23d of May last, Mr. Brockedon gave some account of a new method of projecting shot, which had been discovered by Mr. Sieviere, the sculptor. Mr. Sieviere had furnished Mr. Brockedon with a report of his earliest experiments, and to some of a later date, Mr. Brockedon was an eye-witness. The discovery was accidentally made many years since, by Mr. Sieviere, who was one evening amusing himself with a pewter syringe, which he had converted into a cannon, having closed the discharging end of the syringe, and made a touch-hole. Into this cannon, he put some pinches of gunpowder, and discharged the piston from it, which fell harmless at a short distance; happening to invert the order of firing, by holding the piston, the syringe was discharged with so much violence, as to pass through the ceiling and floor into the chamber above that in which he sat. He was struck with the prodigious difference of effect produced, and immediately had a shot cast, which, in form, was like a mortar: this he fired from a solid mandrel, or bar swung upon trunnions, and capable of elevation and adjustment. His experiment succeeded so entirely, that he was induced to make a shot with radiant bars, which, though they added little to its weight, added much to its power of destruction to rigging, &c. The weight of this shot, which was of cast-iron, was 15 pounds; this was discharged through a bank of clay 6 feet thick, and fell 20 yards beyond it. When fired again, it hit point blank at a distance of 175 yards, and was buried above 3 feet in the bank; the chamber of this shot, with which a touch-hole communicated, was precisely like that of a mortar, and when it was placed for firing upon the mandrel, the shoulder of the chamber at the bottom of the calibre rested upon the end