. The railroad and engineering journal . ever F G, which carries a pencil, G. By thismeans the piston has only one fourth of the motion that it im-parls to the pencil, so that the momentum of the moving parts iscomparatively slight. In order that the pencil may draw a straight line instead of acurved one, a roller is attached to the lever at //. This movesin a curved slot, // /. which causes the end G to move in astraight line instead of the arc of a circle. The levers and allthe parts, are, of course, all made as light as possible, so thattheir weight will have little effect on the motion of
. The railroad and engineering journal . ever F G, which carries a pencil, G. By thismeans the piston has only one fourth of the motion that it im-parls to the pencil, so that the momentum of the moving parts iscomparatively slight. In order that the pencil may draw a straight line instead of acurved one, a roller is attached to the lever at //. This movesin a curved slot, // /. which causes the end G to move in astraight line instead of the arc of a circle. The levers and allthe parts, are, of course, all made as light as possible, so thattheir weight will have little effect on the motion of the indicatorpiston. The paper or card, P P. on which the diagram is drawn, iswrapped around a brass cylinder, K A. This cylinder is madeto revolve part of the way around by a strong twine, L At,which is wrapped around a puUy, A, at the bottom of the cylin-der. The twine is attached to a lever, similar to that shown infig. 38, which receives a reciprocating motion from the pistonof the engine. The twine can, of course, move the cylinder. Fig. 234. Question 362. What is the construction of this instrument? Answer. Fig. 233 represents the Tabor indicator.* Itconsists of a cylinder, B (which is shown in section), into whicha piston. A, is accurately fitted, but so that it will move freelyin the cylinder. The piston-rod C is surrounded with a spiralspring, D, the lower end of which is attached to the top of thepiston, and the upper end to the cylinder cover. When steamis introduced below the piston it pushes it up in the cylinder,and the spring is compressed. If there should be a vacuumbelow the piston, the air above it will press the piston down-ward and extend the spring. This latter occurs only when theindicator is used on condensing engines. Of course the dis-tance which the piston is forced up by the steam-pressure belowit depends upon the amount of pressure and also on the tensionof the spring ; and therefore if a pencil was attached to the pis-ton-rod so that it could mark o
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