1578
THEORY AND PRACTICE OF ENGINEERING
Book II.
coils can be put out of gear by couplings, or by the ordinary methods of disengagingmachinery; one end of the small levers in turning touches the cylinders, which drives theminto the clutches fixed at the other end, and throws them out of gear. The fly-wheelwhich regulates the motion is made proportionate to the cylinder.
When there are a succession of planes throughout a railway, as is the case in some situa-tions, it is necessary at the top of each pair of planes to have two rollers on which therope coils, worked by a stationary steam-engine. Ropes attached to the carriages drawthem up and let them down the inclined plane : each station must be provided with tworope rolls, one uncoiling at each end of the train. When it is required that the carriagesshould descend, the action must be reversed, enabling them to proceed in the opposite direc-tion, or towards the roll at the further end of the train; thus, by an endless rope workingalternately round a cylinder at each end of the railway, a regular transit is maintained. Theropes must always be placed in a line with their work, or the middle of the cylinders mustbe opposite the division of the rails.
Where a line of railway is to be worked by stationary engines, they are placed at regulardistances, each engine drawing the carriage to it from the opposite end, unwinding at thesame time a rope from the roll of the next engine, which in its turn pulls a carriage ortrain in the opposite direction, by re-winding the rope on its former cylinder.
When engines of great power are made use of, four trains of carriages may be drawntowards them by four rope rolls at the same time : on the Liverpool and Manchester linea fixed engine is employed to drag the waggons loaded with merchandise up an inclinedplane of 1 in 22, for a length of 2250 yards: this is effected by an endless rope; at thesummit of the plane is a horizontal wheel worked by a pair of engines, one on each side;the waggons always mounting by one road and descending by the other, so that theyare in a right position for the locomotives^which bring them, or are to continue them ontheir journey. In some instances a horizontal shaft extends across the whole width of therailway, upon which, in the middle of each pair of rails, is a wheel 20 feet in diameter witha groove on its vertical edge. The rope which ascends the plane is passed over the upperedge of the wheel, round the under side, and then nearly to the top a second time, by theaid of a sheeve 4 feet in diameter in front. The rope nearly surrounds the 20 feet wheel,and the adhesion is powerful enough to pull up 80 or 90 tons on a plane with a rise of 1in 100.
Self-acting Planes. — It has not been determined at what angle a plane should be laid, thatwould give to a carriage passing it a regular and uniform motion: to produce this themotion should be greatest at the starting point, so that the body should descend by the lawof gravity with accelerated force at first, and afterwards gradually lessen. The cycloidalcurve has been adopted for this purpose, as giving a diminution of force at the terminationproportionate to the gravity at starting; were the inclined plane regular in its descent, theforce would accumulate with the body that descended it, and carriages placed upon it wouldincrease their velocity when they were required to be at rest. At many of the mines theloaded carriages draw up the unloaded, and then two inclined planes are necessary; but it isexceedingly difficult to decide on the angle at which they should be laid, as it must greatlydepend on its uses and the weights to be drawn, as well as time allowed for the transit.