MODERN STEAM PRACTICE.

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far preferable to intermediate pulleys for taking the motion of thereciprocating part to which the cord is fixed. The cord is attachedto the instrument with a hook and running eye; thus the exact lengthof the cord is easily adjusted. The indicator should, if convenient,be fitted to each end of the cylinder, and a diagram taken off forboth ends, without having a small pipe in communication with bothends of the cylinder; but when a pipe is fitted it must be of suffi-cient size, not less than ^ inch in diameter, so that the pressuremay be the same for both ends. If the pipe is made too small, thefriction of the steam on the internal circumference materially tendsto reduce the pressure on the small piston of the indicator. Forvertical engines the plug-tap, for admitting the lubricant into thecylinder for the lubrication of the piston, is provided with a screwedpart for taking the indicator, while another plug-tap is fitted to thebottom of the cylinder. These taps are screwed into the covers orends of the cylinder. For horizontal engines they can be placed onand screwed into the metal surrounding the steam ports; but itis best when they are fitted into the cylinder itself, or at each endon the covers, or otherwise, as the rapidity with which the steamflows through the passages tends to decrease the pressure actingon the indicator piston, although the actual difference may be veryrninute. Care must be taken that no abrupt bends are made in thesmall pipe connecting the top and bottom of the cylinder with thatof the indicator. Of course there must be a small plug-tap fittedto the pipe, so that the communication from the top is shut off whenthe operator wishes to take a diagram from the bottom end of thecylinder, and vice versa. It is essential that the indicator shouldbe placed vertically, so in some instances large easy bends on thesmall pipe are admissible, but in all cases where bends are usedthere must be provision made for running off the water collectingfrom condensation.

When all is in readiness—the engine going at its accustomednumber of revolutions, and all water in the cylinders and pipesejected, with all the run-off valves shut—the operator turns on thesteam to the indicator, the handle for doing so being provided witha stop, so as to have the passage in the plug-tap full open. Whenthe instrument has made a few strokes the cord can be unhooked■—the diagram has been taken; and it is only necessary to noteon the card the pressure of the steam in the boiler, inches of mercuryin the gauge, the number of revolutions, and the scale adopted.