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for the new engine, his interest was consulted by associating his name with that of Newcomen and Cawley in the patent. But in their future operations, we so completely lose sight of Savery, that it were great injustice to these ingenious men to suppose for an instant that he did any thing but receive his share of the profits of the speculation.

From the moment that Newcomen and his colleague found themselves clearly in possession of the principle, their most assiduous care appears to have been exerted in removing the imperfections of their apparatus; and one deficiency which they supplied in a very early stage was a means to condense the steam without throwing cold water over the vessel, as in Savery's engine. This was an object of great practical importance, as it is extremely probable that the boiler was, in the very first attempts (as it continued to be for nearly fifty years afterwards,) placed beneath the cylinder; and in this arrangement it obviously was impossible so completely to protect the top of the boiler from being splashed by the water thrown on the cylinder, as to prevent a condensation of the steam with which it was filled, and which it was essential to preserve at a high temperature.

Instead of throwing cold water on the cylinder, c, as in the diagram, Newcomen surrounded that vessel with cold water, and by this means every part of the surface was exposed to the cooling influence. The steam cylinder was thus placed as it were within another, and the space x, between them contained the condensing medium. (Figure marked NEWCOMEN, A.) But short experience would show, that this contrivance could only be practised with effect under certain circumstances. The practical inconvenience

which resulted was, that the water which cooled the steam, itself became heated in the process, and was thus unfit to produce the effect which it was introduced into the concentric space to perform. It was also necessary that, when the cylinder was filling with steam, the space between it and the outer vessel should either contain water, nearly of the temperature of the steam within, to prevent condensation, or it should be entirely empty. Means, therefore, were to be taken to supply cold water with great rapidity when the condensation was to be produced, and, of course, to withdraw with equal rapidity that portion which had become heated by its contact with the hot cylinder.

The cistern for the cold water, m, (in the figure. marked NEWCOMEN B.) could not be more conveniently placed than over the cylinder, and a pipe, n, conducted the water from it into the space r, formed by the casing. Another pipe, h, conducted that which had become heated into the reservoir, k.

The steam which was condensed, and the injection water, formed within the cylinder a quantity of hot water, which, although of small bulk when measured after one or two condensations, quickly accumulated beneath the pistons when the machine was in action, and would, by its doing so beyond a certain limit, entirely stop its motion. To carry this off, a pipe, i, was inserted into the bottom of the cylinder, and conveyed downwards, and its end was inserted into a cistern, y. In adjusting this pipe, attention was also to be had to the pressure of the atmosphere; for unless it were of sufficient length, as it communicated with a vacuum, formed at each stroke under the piston, the water would be forced from the cistern into the cylinder instead

of falling from it. This pipe was therefore made to descend to a depth of about 30 feet below the bottom of the cylinder.

Still the air, which might find its way into the cylinder by the sides of the piston, or which, rising from the water into the boiler, mixed with the steam, was disengaged when the vapour was condensed, was also to be extracted from this vessel; this is found in the very earliest engines to be done by placing a pipe, s, at the lower part of the cylinder, and opening into the atmosphere, having a valve placed at its extremity, opening upwards, and inserted in a sort of cap, containing water. The descent of the piston compressing the air, made it raise this valve*, and as soon as it had escaped, the water which lay over it sufficed to make the valve airtight. Some authors state that this air was expelled along with the water through the descending pipe, but this must have been in all cases inconvenient, and in many impracticable.

A stream of water was also allowed to flow upon the piston, in order, by interposing a denser substance than air, to make the piston still more air-tight than it could be by the packing.

The junction of the boiler and steam-cylinder was made by a pipe t, proceeding from the top of the one, and inserted into the bottom of the other, having a cock, e, to interrupt the flow of steam at pleasure. And the height of the water in the boiler was ascertained by the same means that Savery had adopted, using two pipes of different lengths, which he called Gauge pipes, 2.

"This is called the sniffing valve, because the air makes a noise every time it blows through it like a man sniffing with a cold."-p. 474. vol. 11. Desaguliers' Experimental Philosophy.

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COUNTERPOISE.

It has already been observed, that from their first trials, Newcomen and Cawley operated with steam, whose temperature never exceeded that of boiling water; and the vapour was used strictly as a means of forming a vacuum. The weight of the piston, its friction, and the friction of the axis of the balance-beam, and the resistance of the pumps, had, therefore, to be overcome by other means, and the counterpoise, w, was an effective and obvious one; this was a weight, hung on the balance-beam, generally on the pump-rod, as shown in the figure.

The operation of this improved apparatus is very simple. When the water has been raised to the temperature of 212 degrees, and the cavity of the boiler filled with steam, the cock, e, is turned, and a communication is thus opened between the cylinder and boiler; and the counterpoise draws the piston to the top of this vessel. When the piston is in this position, the cock, e, is turned to its first position, and the further flow of steam is prevented. Cold water is now allowed to fall through the pipe, n, proceeding from the cistern into the space between the cylinders, and filling it, condenses the steam under the piston; the weight of air resting upon it, presses it downwards into this vessel, which elevates the weight on the other end of the beam, or the water in the pumps. When the piston has reached the bottom of the cylinder, or as it is termed, made its stroke, the steam-cock is again opened, the cistern-cock shut, and an equilibrium being thus restored between the two sides of the piston, the counterpoise as before acts to pull it to the top of the cylinder, and the apparatus is again ready to make another stroke. At the instant when the piston has nearly arrived to the limit of its stroke,

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and before the steam-cock is opened, the coldwater pipe is shut, and the cock h, permitting its fall into the cistern, opened, so that when the steam was admitted into the cylinder, the annular space was empty. In another arrangement, the water which had been heated by the previous stroke was allowed to remain, until the piston had been raised nearly to its limit; it was then allowed to flow into the reservoir, and was replaced by the cold water from the cistern. The water arising from condensation escapes by the pipe, i, and the air by the other pipe, s.

The waste of water in the boiler by evaporation was supplied by Newcomen in a simpler manner than in Savery's engine; and part of the heat which was lost by the condensation of the steam in the Captain's machine, was saved by replenishing the boiler with the water which had been heated between the cylinders; by conducting it into a pipe rising from the boiler, or pumping it into this pipe from the reservoir, into which the heated water fell both from the inside and outside of the cylinder.

It were almost superfluous to notice the prodigious difference in safety between this machine and that of Savery; and to point out the variety of situations, in which the lever engine must be a more convenient agent than its rival apparatus. . But there were circumstances demanded in the construction of the one, which were not essential in the other, which were greatly in favour of that the most deficient in principle.-One of the greatest objections attached to Newcomen's apparatus, was the accuracy of workmanship which was demanded in the construction of the cylinder and piston, and which could not be obtained by any of the mechanical means then resorted to: