. The steam-engine and other heat-motors . on should be below the lineof motion of the cross-head one-half the versine of one-half thearc of oscillation of the lever. In other words, the driving-studin midposition is as much below the line of motion of the cross-head in midposition as it is above it on the two ends of the — Figs. 30 and 33 show different designsof reducing-wheels. When properly made and handled theygive accurate results. They can be tested by moving the pis-ton inch by inch, being careful to take up all lost motion andmeasuring the corresponding rotatio
. The steam-engine and other heat-motors . on should be below the lineof motion of the cross-head one-half the versine of one-half thearc of oscillation of the lever. In other words, the driving-studin midposition is as much below the line of motion of the cross-head in midposition as it is above it on the two ends of the — Figs. 30 and 33 show different designsof reducing-wheels. When properly made and handled theygive accurate results. They can be tested by moving the pis-ton inch by inch, being careful to take up all lost motion andmeasuring the corresponding rotation of the drum. In makingcalibrations of this or any other sort the student should be care-ful to see that the practical conditions are identical with thetest conditions. An indicator reducing motion was calibrated in J60 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. the above manner and gave perfect reduction when the enginewas jacked over, but gave imperfect results when the enginewas working. This resulted from attaching the reducing motion. Fig. 33. to the lower guide, which, when the engine was under full load,was found to vibrate enough to distort the card. Pantographs theoretically give a perfect reduction. Numer-ous joints must be avoided, as each must be free from lost motion. Fig. 34 shows a pantograph device at midstroke. This ismade of bar iron nicely riveted together. The indicator-cordmay be attached at b. The end a is attached to a pin on thecross-head. The fixed fulcrum is at c. a, b, and c must alwayslie in the same straight line, and ed and bn must be paralleland equal to fg. Also af + nf= stroke of pistons by the lengthof the indicator diagram. * * Quoted from Practical Instruction for Using Steam-engine Indicator^Crosby, page 32. STEAM-ENGINE INDICATOR AND ITS CALIBRATION. 61 In Fig. 35, / is a rod moving in a slide parallel to the pis-ton-rod. Link bd is attached to /, and link ae to the , b, and c must always lie in the same straight line, ae + bdan
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