186 COMPARISON OF ENGINES. ambitious display of auxiliary mechanical detail, from his great experience in general mechanism, he saw, that this extreme simplicity was one of the best properties which could be possessed by machines constructed on any principle, and that this would, in fact, form one of its strongest and best claims to the introduction of this invention into general practice. Neither did it escape his penetration, that the powers of this apparatus, under certain conditions, could be increased or diminished at pleasure, without demanding a corresponding enlargement or diminution of the cylinder, and that this variation in its energy might be produced without inconvenience, and with a rapidity which could leave nothing further to be wished for. Besides, the entire apparatus was not only simpler in form than Newcomen's, its parts fewer, but no greater delicacy of workmanship was required in their construction. With the exception of Newcomen's invention, no motion had been produced by means of the intervention of a piston, which could be considered as at all adapted to practice. By Newcomen, as we have seen, steam was applied (instead of an air-pump) to make a vacuum under the piston, in order to permit its fall by the weight of the atmosphere; he was careful that the elastic force of the steam should never be called into action, it exerted, therefore, no direct action on any part of the apparatus in contact with it. In illustrating the principle of Papin's digester, Leupold was led, by a very obvious step, to view what was considered to be its greatest defect, as opening a source whence might be obtained not * P. 403, vol. 111. Theatrum Machinarum. HIGH-PRESSURE LEVER ENGINE. 187 only a more powerful but a more portable mechanical agent than had yet been moulded from the elasticity of steam. A piston raised by vapour of a high temperature might be placed at the end of a lever loaded with any weight, and instead of condensing the vapour which performed this office, it might be allowed to escape (as in his second scheme) into the atmosphere; and where a continuity of effect, as in pumping water, was desirable, two cylinders might be connected, so that when the steam from the one was escaping into the air, and, of course, producing no effect, in the other it should be forcing water into the reservoir: this, not differing greatly in a general view from his scheme already described, may be considered as the first successful attempt at the combination of, what has been called the high-pressure lever engine. The view given of this contrivance by its inventor is shown in the engraving (marked LEUPOLD.) The two steam recipients, or cylinders, each have a piston, a, b, fitted into them, and which are attached to a lever vibrating on its fulcrum, having a pump-rod fixed to the other end. A communication is opened with the boiler by means of a channel, d, and the under side of the piston, a, and the expansion of the vapour raises it to the top of the cylinder; this presses the pump-rod (placed at the other end of the lever) downwards in the pump-barrel, and the plunger or piston being solid, the water beneath it is pressed to the required height up the pipe, i. When this piston has been raised to the top of the cylinder, the fourway-cock is turned round, and the channel, d, opens a passage for the steam to flow from under the *P. 403, vol. 111. Theatrum Machinarum. 188 FOURWAY-COCK. piston, a, into the atmosphere; and, at the same time, the channel, e, is brought into a position similar to that which d had occupied, and thus allows steam from the boiler to enter under the piston, d, this is now elevated in its turn; c, is the boiler; h, the furnace.* In the two last figures, the return of the water which has been raised is prevented by the usual means of a puppet-clack, or valve, opening up. wards. The candid and disinterested Leupold confesses that he owes the idea of the fourway-cock,+ and the use of very elastic steam to raise a piston, to a perusal of the writings of the ingenious Doctor Papin, and ascribes to him all the merit of his combination. But, without wishing to detract the smallest portion of praise from the labours of that most ingenious, but neglected philosopher, it were injustice to deny Leupold the praise of erecting a valuable superstructure on a foundation, which, in truth, should be said to have been indicated rather than laid by the industrious Papin.‡ The operation of the fourway-cock will be easily understood from the figures. The channels from the cylinders and from the boiler are fixed, and those in the moveable cylinder are perforated in a curved direction, so that they may be turned either to continuea communication between the recipient p. 90. * See The valve below the plungers in the engraving should have been shown reversed in position. A similar idea occurred to Mr. Watt." I intend in many cases to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner as the pressure of the atmosphere is employed in common fire-engines. In cases where cold water cannot be had in plenty, the engines may be wrought by the force of steam only, by discharging the steam into the open air after it had done its office."-Specification of Patent, 1769. MEY AND MEYER. 189 and the boiler, or between the cylinder and the atmosphere. Leupold took it from Papin's airengine, but, as usual in his hands, it received considerable improvement. Some insulated attempts at minor improvements may here be noticed. Beighton formed a table of calculations, in 1721,* for the proportions of some of the details; but, in other cases, a repetition of what had been long done in one country, was published as an improvement by a native of another. Mey and Meyer's apparatus,t of which an excellent engraving and detailed description were given by the French Academy of Sciences in 1726, was then in action at Passy, near Paris. It is similar to that which has been described by Desaguliers. Bosfrand shortly afterwards presented to the same society, drawings and a description of an engine, containing what he considered improvements wanting to be made on Mey and Meyer's. One of the most notable of these, was a valve inserted into the side of the cylinder, and near to its top, which was closed by a weight, hung from the end of a steel-yard-this was a contrivance to allow the steam to escape when it was "too strong in the cylinder!"-his sniffing-clack was placed at the bottom as usual. About equal in merit to that which has now been detailed, are some other minor additions found in this, and not in the engines in common use. The whole description gives a good idea of the ignorance of the first principles of the machine; which, at this time, prevailed even among persons generally accounted intelligent and well-informed. Bosfrand's other engine, of which, also, a good * P. 316, Ladies' Diary, 1721. P. 209, tom. IV. Machines Approuvées. 190 MEY AND MEYER. engraving is given in the same volume, is similar to that which has been described, as claimed by Desaguliers and made by him for the Czar Peter, nearly ten years before-with the alteration of forming the two gauge-pipes, to be opened and shut by one cock, on the construction of the fourway cock of Papin, |