Images de page
PDF
ePub

66

"other cases I apply those engines of my invention which "act forcibly both in the ascent and descent of their pistons, "and by means of the rotative motion in figure 20th,* or of 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

66

66

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.

66

66

primary axis, which is immediately moved

And upon the 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 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

66

66

* A sun-and-planet wheel.

66

many sizes and variously loaded, the engines must be made "powerful in proportion. But to drive a carriage containing "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

66

[graphic]

Working Model of a Locomotive Engine made by Mr. W. Murdock in 1784.

"force of the steam in the boiler must occasionally be

66

66

equal to the supporting a pillar of mercury thirty inches high."

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. In that year, the model of the locomotive was repeatedly seen by his friends and various persons in the neighbourhood, drawing a small model waggon round a room in his house at Redruth; and of its early performances the following anecdote has been preserved:-" At the time that Mr. Murdock was making his

66

[ocr errors]

experiments with his locomotive engine, he greatly alarmed "the clergyman of the parish of Redruth. One night, after "returning from his duties at the mine, he wished to put to "the test the power of his engine; and, as railroads were “then unknown, he had recourse to the walk leading to the "church, which was situated about a mile from the town. “This was rather narrow, but kept rolled like a garden walk, "and bounded on each side by high hedges. The night was "dark, and he alone sallied out with his engine. He lighted "the fire or lamp under the boiler, and off started the loco"motive, with the maker in full chase after it. Shortly after "he heard distant shouting, like that of despair; it was too "dark to discern objects, but he soon found that the cries for "assistance proceeded from the worthy pastor, who, going "into the town on business, was met in this lonely road by "the fiery monster, whom he subsequently declared he took "to be the Evil One in propriâ persona. Whoever has been on one of our modern rail-roads on a dark night, and seen an approaching train-although now no novelty-may easily imagine what effect the awful sight would have on "the nerves of an elderly gentleman of the last century; "and, although the demon was in this case of small dimen"sions, yet it was a total stranger, and quite unlooked for in "such a locality.” * With a spirit-lamp for a furnace, its cylinder attached to the boiler, and its piston-rod working a beam that turned the driving-wheels by a crank, the model 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 which have since been erected in H. M.'s 91-gun screw steam-ship the "James Watt;" and by its side was placed another interesting model, 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

66

66

*From Mr. Buckle's notice of Mr. Murdock, already cited.

[ocr errors][merged small]

cylinder remains, a valued heirloom, in the family of Mr. Murdock.*

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 "working-beam, which in "this case may be short. "I do not know that the

66

axle of rotative
movement.

[blocks in formation]

"lock and unlock the wheels which connect them together, "so as to make the carriage go faster or slower at pleasure,

[ocr errors]

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

*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
vol. iii. plates XXIX. and XXXIV.
† 17th August, 1784.
27th August, 1784.

[ocr errors]

66

66

"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, 4802 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

66

1 times as dense as the common steam, therefore there "must be a surface of 12 feet exposed to the fire, if not " more; let us leave the form of the boiler out of the case at "present. The surface of 12 square feet which we suppose "to be exposed to the fire, must be covered with a shell of "water of some thickness, which, upon the average, I shall

« PrécédentContinuer »