Chap. XXI. STEAM CONSIDERED AS A MOVING POWER.
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To find the length which should be given to the radius bar, when the length of the beamfrom the centre of motion is to half the length of the stroke as S is to 2 : from threetimes half the length of the stroke, subtract twice the length of the parallel bar, and
PARALLEL MOTION,
Fig. 2028.
PARALLEL MOTION.
Fig. 2029.
PARALLEL MOTION.
multiply the difference by half the length of the stroke ; this product divided by ’343M6times the length of the parallel bar, and the quotient added to the length of the parallelbar, gives the length of the radius bar. The radius bar and the parallel bar should beof equal length, when twice the parallel bar is equal to three times half the length of thestroke.
When there is no assigned proportion between the length of the stroke and the radiusof the beam, the length of the radius bar is thus found: first, from the length of theradius of the beam, subtract twice the length of the parallel bar, and multiply the differenceby the square of half the length of the stroke ; secondly, find the square root of the differencebetween the square of the length of the radius of the beam and the square of the halflength of the stroke, and subtract this root from the length of the radius of the beam, andmultiply the difference by twice the length of the parallel bar. This product becomesa divisor to the number found by the first part of the operation ; the quotient obtained,added to the length of the parallel bar, gives the length of the radius bar.
Cartwright's Parallel Motion , (figs. 2030, 2031.) consists of two toothed wheels, which workin each other, and from corresponding points in their circumference two connectinglinks unite at the extremity of a cross bar, to the middle of which is joined the piston-
1 M