66 post-chaise will not be more than 300 lbs., water and all, " and it will be contained in very small compass." In the seventh" new improvement," however, set forth in the specification of his patent of 1784, Mr. Watt described the principles and construction of "steam-engines which are "applied to give motion to wheel-carriages for removing "persons or goods, or other matters, from place to place, in "which cases," he says, "the engines themselves must be portable. Therefore, for the sake of lightness, I make the "outside of the boiler of wood, or of thin metal, strongly "secured by hoops, or otherwise, to prevent it from bursting by the strength of the steam; and the fire is contained in a "vessel of metal within the boiler, and surrounded entirely 66 66 66 by the water to be heated, except at the apertures destined "to admit air to the fire, to put in the fuel, and to let out "the smoke; which latter two apertures may either be situ"ated opposite to one another in the sides of the boiler, or "otherwise, as is found convenient; and the aperture to "admit air to the fire may be under the boiler. The form "of the boiler is not very essential, but a cylindric or globular "form is best calculated to give strength. I use cylindrical "steam-vessels with pistons, as usual in other steam-engines, " and I employ the elastic force of steam to give motion to "these pistons, and after it has performed its office I discharge "it into the atmosphere by a proper regulating valve, or I "discharge it into a condensing vessel made air-tight and "formed of thin plates or pipes of metal, having their out"sides exposed to the wind, or to an artificial current of air "produced by a pair of bellows, or by some similar machine 66 66 wrought by the engine or by the motion of the carriage; "which vessel, by cooling and condensing part of the steam, "does partly exhaust the steam-vessel, and thereby adds to "the power of the engine, and also serves to save part of the "water of which the steam was composed, and which would "otherwise be lost. In some cases I apply to this use 66 engines with two cylinders which act alternately; and in "other cases I apply those engines of my invention which "act forcibly both in the ascent and descent of their pistons, 66 66 66 "and by means of the rotative motion in figure 20th,* or of 66 any other proper rotative motion, I communicate the power "of these engines to the axis or axle-tree of one or more of "the wheels of the carriage, or to another axis connected "with the axle-tree of the carriage by means of toothed "wheels; and in order to give more power to the engine "when bad roads or steep ascents require it, I fix upon the "axle-tree of the carriage two or more toothed wheels of "different diameters, which when at liberty can turn round freely on the said axle-tree when it is at rest, or remain "without turning when it is in motion; but, by means of catches, one of these wheels at a time can be so fixed to the axle-tree, that the axle-tree must obey the motion of the "toothed wheel, which is so locked to it. And upon the "primary axis, which is immediately moved by the engine, "or which communicates the motion of the engine to the "axle-tree of the carriage, I fix two or more toothed wheels "of greater or lesser diameters than those on the axle-tree, "which are moved by them respectively, so that the wheels "on these two axles having their teeth always engaged in one another, the wheels on the axle of the carriage always 66 move with the wheels on the axle of the rotative motion, "but have no action to turn the wheels of the carriage ex"cept one of them be locked fast to its axle-tree,-then the "latter receives a motion faster or slower than that of the "axle of the rotative machinery, according to the respective " diameter of the wheels which act upon one another. In "other cases, instead of the circulating rotative machinery, "I employ toothed racks or sectors of circles worked with reciprocating motions by the engines, and acting upon "ratchet wheels fixed on the axles of the carriage. And I "steer the carriage, or direct its motion, by altering the angle "of inclination of its fore and hind wheels to one another by means of a lever or other machine. As carriages are of "many sizes and variously loaded, the engines must be made "powerful in proportion. But to drive a carriage containing 66 66 66 * A sun-and-planet wheel. "two persons, will require an engine with a cylinder seven "inches in diameter, making sixty strokes per minute of one "foot long each, and so constructed as to act both in the "ascent and descent of the piston; and the elastic force of "the steam in the boiler must occasionally be equal to the supporting a pillar of mercury thirty inches high." 66 Working Model of a Locomotive Engine made by Mr. W. Murdock in 1784. Also in 1784, Mr. Murdock made a working model of a locomotive engine upon the principles so specified by Mr. Watt, which performed well, and is still in existence. With a spirit-lamp for a furnace, its cylinder attached to the boiler, and its piston-rod working a beam that turned the drivingwheels by a crank, it was placed in the Great Exhibition of 1851, where it attracted much notice. It stood among the "machinery at rest," on the colossal marine engines of 700 horse-power, manufactured by Messrs. James Watt and Co., which have since been erected in the fine 91-gun screw steam-ship the "James Watt;" and by the side of that * See the Official Catalogue, vol. i. p. 211. interesting little model was placed another, also of diminutive size, of a steam-engine with an oscillating cylinder, invented and constructed by Mr. Murdock in the year 1785. The model of the locomotive engine is now in the possession of Messrs. James Watt and Co.; that of the oscillating cylinder remains, a valued heirloom, in the family of Mr. Murdock.* 66 66 In reference to this specification, Mr. Watt writes to Mr. Boulton,+ "I have given such description of engines for wheel"carriages as I could do in the time and space I could allow "myself; but it is very defective, and can only serve to keep "other people from similar patents." And, ten days later,‡ "I wrote to you last night, and now sit down to give you some "of my ideas on the wheel-carriage scheme, and have there"fore annexed that article of the specification, by which you "will see the general idea. The engine may either be con"nected with the rotative motion by a working-beam, or may "be placed directly over the secondary axle, and work the "rotative motion by means of two rods coming down on each "side of the cylinder from a cross-bar on the top of the piston-rod, guided perpendicularly by a sliding frame; but "I am inclined to prefer a 66 working-beam, which in "this case may be short. "I do not know that the "organ-pipe condenser will "make much vacuum, but "it may, by the help of "the bellows, condense, and "save most of the water. "On the side you have a "sketch of the two axles, "and of the means I use to a axle of rotative movement. axle of carriage. "lock and unlock the wheels which connect them together, "so as to make the carriage go faster or slower at pleasure, Both of these curiosities of the engineering art were, by the permission of their respective proprietors, delineated and engraved for the 'Me 'chanical Inventions of Watt;' see 66 66 66 66 66 or, at least, to have more or less power at will. The piece (a b) slides in a hollow, and two slits in axle of "the carriage; when 6 is in the place drawn, the rotative "motion can turn without moving the carriage; but when "b is placed so as to be in a slit which is in one of the wheels, then the wheel will cause the axle to turn round or "to break b; and b is always disengaged from one wheel "before it is locked to the other. As to the size of the cylinder, boiler, &c., I calculate that, suppose the power "necessary to move a post-chaise on a plain to be 80 lbs. weight, and the chaise to move at the rate of 4 miles per "hour, or 6 feet per second, let the moving-wheel be 4 feet " diameter, then it will make 1 revolution in 2 seconds, and "if the engine makes 60 strokes per minute, it will make one "revolution for 2 strokes; but as the rotative motion will "make 2 revolutions per stroke, it will make 4 revolutions "for each turn of the wheel of the carriage, and 80 lbs. × "6 feet 480 lbs. 1 foot high per second, and supposing the "stroke of the engine 1 foot long, 480÷2 must be its power 240 6 lbs. on inch to a 7-inch cylinder; but as going "up hills it will require a power of 400 lbs. to drag the "chaise up, the power in these cases must be increased 5 times, that is, the axle of the carriage must make only 1 "turn for 20 turns of the rotative axle, and will then move "only 12 feet in 10 seconds; but this inconvenience may be "something lessened by letting the steam get stronger at "such times. 66 66 = "A cylinder of 7 inches diameter and 12-inch stroke will "take something more than a foot of steam per double-stroke, "supposing it to be working with a condenser; consequently "it would take 30 cubic feet of steam per minute = 1800 "feet of steam per hour, which, supposing it to be equal to " 1 cubic foot of water, would require a boiler of 8 feet sur"face exposed to the fire to make any tolerable performance "in respect of fuel; but as we can depend on no aid from "condensation, we must suppose this steam to be at least 1 times as dense as the common steam, therefore there "must be a surface of 12 feet exposed to the fire, if not 66 |