Figure 4 (fi/. 82), which represents a modern Watt's engine of the most perfected type, exhibits only a portion of the parallelogram con necting the piston-rod with the oscillating beam. This Figure also shows the solid frame consisting of six columns, an iron foundation, and an archi trave-like upper support, in which Watt enclosed his perfected machine, thereby considerably increasing its solidity.
The jacket in which Watt enclosed the cylinder to prevent the cooling of of the steam therein is more plainly recognized in Figure 6, which rep resents in section the steam-cyl hider with jacket (K) and the air-pump with the condenser J concentrically arranged around it. II is the frame carrying the engine, and C, I), F, G a mechanism replacing Watt's parallelogram. Beighton used for feeding the boiler the heated water of condensation, when it was soft; but when it was hard, lie heated the feed water by a coil passing through the condensing-water. The first inven tions by Watt were based less upon the properties of steam than upon the phenomena of heat, because by the peculiar construction of the condenser and of the steam-jacket, as well as by the closure of the upper portion of the cylinder against the entrance of cold air, he prevented the losses which, in an economical respect, made Newcomen's machine practically useless for many purposes. He also later on planted the germ of an improvement which occupies the foremost rank as regards the advantageous application of the steam-power, by the utilization of the expansive action of steam. This action commences when the supply of steam is shut off and the steam in the cylinder is left to itself before the piston has arrived at the end of its stroke. Though the steam from the boiler is shut off, the piston continues to be pushed forward by the steam through the expansive force which constantly becomes weaker. Thus, for instance, a given quantity of mechanical effect is produced by the gradual expan sion of the steam to double its normal volume, and consequently to half the normal tension that would otherwise be produced by double the quan tity of steam. For the purpose of ascertaining the exact amount of this gain of effect it is necessary to determine the specific relation existing between the tension and the volume of this shut-off expanding steam, a problem of physical science on which much ingenuity has been expended since Watt's time.
s ascertain empirically the complex result of all these and other component activities on a machine, Watt devised and used an instrument called an "indicator," which, as improved by Richard, is shown iu its modernized form in Figure io (bl. So). This instrument when
connected with the inner space of the steam-cylinder indicates graphically, by a closed curve upon a strip of paper, the varying steam-pressures suc ceeding one another during the duration of a stroke. This is effected by means of a piston which on the one hand is connected by a spring with the indicating mechanism, and on the other hand is subjected to and actu ated by the same varying steam-pressure in the cylinder as is the large piston. From the diagram traced by this instrument the effect of the steam during a stroke can be calculated, a counter (pl. 82,fig. r) con nected with a rotating portion of the machine indicating the number of strokes made in a given time, and a water-meter (fig. 2) measuring the quantity of steam conducted into the cylinder during the time. These observations form the elements for the calculation of the degree of effect or utility of the steam-engine, and from them also the capacity in horse power and the consumption of steam per indicated horse-power are cal culated.
apparatus, the dynamometer (see p. 385), is used to indicate the effective or actual amount of power given out by the engine. The dynamometer is fastened upon the shaft of the fly-wheel, and its indication of the effective result in horse-powers, when subtracted from the indicated horse-power calculated from the indicator curves, shows the amount of mechanical force consumed in moving the mechanism of the engine by friction and inertia. In this manner it has been determined that modern machines carefully constructed according to Watt's system produce six times as much effect with a given quantity of coal as New comen's.
The development of the steam-engine to its completed form, as shown in Figure 4 (pl. 82), was not, however, Watt's work alone. As already mentioned, the three-port slide-valve, described in Figures II and 12 (pl. 8o), was invented by Murray, while the crank mechanism and the fly wheel originated with other English inventors and mechanics. It was but natural that Watt and his co-workers should only gradually and cau tiously, step by step, have developed the actual steam-engine from the atmospheric motor of Newcomer. The pressure they employed was never much above that of the atmosphere, and they even attempted to have passed an act of Parliament forbidding the use of high pressure for the reason that it endangered the lives of the public.