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when this happened it invariably was found that "the meat was spoiled." A Dr. King, "for greater security and conveniency, caused the lever to be fitted with a joint, so that it must always fall upon the pipe, and there is no danger that the valve (or stopper) may slip off and spoil the operation."*

"But an engine which was made for the laboratory of his majesty, Charles II., of blessed memory, has the advantage to have no hole to the cover, which in the first engines caused some trouble, besides some danger," which probably arose from the boiling water being forced upwards; but even that was preferable to the danger in the king's engine of the cook being blown to pieces by the bursting of the boiler, instead of being scalded, as in the first apparatus. "To know," continues Papin, "the degree of heat in this boiler, instead of a thermometer I use another way, very easie, and yet exact enough for all my uses. I hang a weight to a thread about three feet long, so that every swing makes a second, and I let fall a drop of water into a little cavity, made for that purpose at the top of it, (the roof of the boiler,) and I tell how many times the hanging weight will move to and fro before the drop of water is quite evaporated; and I take care that the place where I put the drop may be clean, because a little grease will considerably hinder its evaporating."

* Continuation of the New Digester, p. 53, 1687. † P. 3, ibid.

The drop of water drying up in five seconds indicated a degree of heat equal to ten pressures; in three seconds equal to nine pressures; he had built no furnaces for his boiler, but always had set it" in a chimney corner, and put the fire between the chimney and the engine." Dr. King caused a brick furnace to be built on purpose, thinking that would lessen the expense for coals. "But I found, contrary to my expectation, that the expense is much greater in his furnace; the

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In 1685, the same philosopher exhibited a model of a machine for raising water, "and having seen it practised several times, that after the discovery of some new problem the inventor propounds it as a riddle, to stir up those that are ingenious in the same kind of learning, and make them find sometimes better things than what is propounded." Papin thought "he might do the same with his way for raising water, which he thought surely to be new, since it is not used, in considerable occasions, where it might be of great advantage."

The solutions which were given by three persons who made the attempt, not fulfilling the conditions

reason of which probably is, because in his furnace the coals did not at all touch the engine, but remained a little distance below; as in ordinary sand furnaces, the coals do not touch the pot, but in my chimney the coals touch the engine almost all along, and thereby may the better heat it. It is, therefore, likely that it would be better to build furnaces so as to have the coals touch the engine all along one side." Continuation of the New Digester, p. 53.

He found "that the quantity of coals required to boil beef was nearly two-sevenths greater than that required to boil mutton:" his valves were made tight with paper-leather melted; sometimes he softened the biggest bone of a leg of beef without spoiling the meat. With steam of nine pressures he boiled "a piece of a breast of mutton with six ounces of coals;" a breast of beef under nine pressures was cooked with six and a quarter ounces: from his experi ments he concluded, "that the more briskly we press the fire, the more effect it produceth with the same quantity of coals. The greater the inward pressure is, the greater effect is produced by the same heat in the same time; that it is near the same to press the fire with four and a half ounces of coals, so as to dry away a drop of water in ten seconds, and then let the fire go out of itself; or to press the fire with six or seven ounces, and then take it all off as soon as a drop of water dries in three seconds: the greater the inward pressure is, the less quantity of coals is required to give a certain degree of heat."

* Philosophical Transactions, vol. xv. p. 1093.

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of his problem, in a few months afterwards he gave a description of his model, from which it appeared, that the water was raised by rarefying the air in the vessel into which it was impelled by the pressure of the atmosphere on the water in the cistern. The mode by which he rarefied the air was carefully concealed. In two of the solutions the same effect was produced by condensing it.

Thus far the scheme may be considered an ingenious trick; yet an useful air was given to his proposition by showing how a series of exhausting vessels might be connected so as to raise water from considerable depths;* and a suggestion for communicating motion by means of air to a great distance, which grew out of a discussion respecting its practicability, was conceived in an original and philosophical spirit. Suppose, for example, that it was required to raise water out of a mine, and that there was no river to turn a wheel to move the pumps nearer than a mile. Papin proposed to place two cylinders fitted with pistons near the water-wheel, and other two at the mouth of the mine; these were to be connected by a pipe. The action of the pistons moved by the wheel compressing the air in the cylinder and in the pipes throughout its whole length, Papin thought, that when the pistons at the one end were depressed by the communication of pressure, those at the other end would be elevated. But although the pumps, moved by the water-wheel, condensed the air, the pistons at the mine stood still. And the failure arose from a property of air, which, however familiar to Papin as a mechanical philosopher, was overlooked in his apparatus. The air itself was a very compress

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ible body, and in his mechanism it was not compressed sufficiently to offer such a resistance to further condensation, as was necessary to move so great a weight as that placed on the pumps of a mine. Of two methods of remedying this defect, the one which happened to occur to Papin made his machine impracticable; the length which he found was required for his compressing eylinder was altogether preposterous.

Great as his reputation was in England, he failed in getting patrons to give a trial to his apparatus. But when he returned to France, and after he was driven from it by the revocation of the edict of Nantes, and had settled, in 1687, at Marpurg, in Germany, he was employed by some persons of large fortune to erect machines on this principle at Auvergne, and in Westphalia, to drain mines. The result had been predicted by Dr. Robert Hooke and others; the failure was complete. It was in vain that he attempted to get over the difficulty by increasing the capacity of the cylinders and diminishing that of the connecting pipe, the hopes of, by this means, keeping his cylinders of a moderate size were still to be disappointed. He now reverted, in part, to his first idea, constructing the pistons with valves and cocks similar to those of an air-pump, and instead of compressing the air in the cylinders, he formed a vacuum throughout the entire apparatus by the action of the water-wheel, in order that, by exhausting the cylinders under the pistons near the mine, the pressure of the atmosphere should

*Nouvelles de République des Lettres, December, 1686. A Mons. Nuis urged some objections to Papin's scheme, which were answered in the Phil. Trans. No. 186, p. 263; from this it appears that his vacuum was equal to a pressure of twelve feet of water.

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act to impel them downwards, and thus produce the required motion. His modification of the apparatus to accomplish this object may be shortly described.

The pistons at the mouth of the mine were attached to ropes, which were wrapped several times round an axle, or horizontal shaft, in opposite directions, so that when the one was coiling and drawing up its piston, the other was unwinding and allowing the other to descend. On this shaft a large wheel was also fixed, having a cord on its circumference carrying a bucket at each end, which alternately rose and descended as the piston-ropes were wound or uncoiled. The pistons near the water-wheel were attached to its axle in a similar manner, and arranged so, that when one piston was at the bottom, another was at the top of its respective cylinder; a single pipe formed a communication with the two sets of cylinders, branching at its termination to each cylinder, and having a double passaged or fourway cock at their junction with the conveyance pipe, to admit the air, and to shut it off from beneath each piston alternately.

By the motion of the water-wheel a vacuum was produced in the cylinders under the pistons and in the conveyance pipe; that piston near the mine cylinder, which was at the top of its vessel, having a communication with the connecting pipe, and the air being withdrawn from beneath it, was pressed downward by the atmosphere, this moving the axle drew the other piston upwards, the air being admitted under it at the instant it was shut off from the other; the cock is now turned ; a communication is opened with the machines et autres sujets philosophiques, par M. D. Papin, Dr. en Méd. A Cassel. 1695.