Chap. XI.
MECHANICS.
993
Fig. 1474.
Fig. 147-1. By means of two lengthsof chain attached in opposite direc-tions to each of the rods m,n passingthrough the tenons r, r, the circularalternate motion of the balance b , towhich the ends of the chains are fixed,communicates an alternate rectilinearmotion to these rods.
Fig. 1475. is the very well knowntool, the common drill : a is therod, b the cord, c the cross pieces, dthe fly, e the muffle or socket, whichtogether are called the stock, g thecutting tool or drill.
Fig . 147G. is a motion appliedto pumps; all is a rod slidingbetween the guides c y d: the leveref turning on its axis g communi-cates by means of a rod eh itsalternate circular motion to therod ab, which has an alternate recti-linear motion.
Fig. 1477. Parallelogram em-ployed in double-acting steam en-gines to transform the alternaterectilinear motion of the inflexiblepiston-rod to the circular alternatemotion of the balance beam : abedis the parallelogram attached to thebeam by the points a and c fixed to this beam, but the sidesof the parallelogram can change their inclination with regardto each other by means of their hinged extremities, that is tosay, the boxes or collars embracing the horizontal axes: theseaxes at a and c are in the same plane with the centre or axisof rotation of the beam : the angle d of the parallelogram isalways kept at a constant distance from the point e, by meansof an iron rod with a box or collar at its extremity, whichembraces the axis passing through d.
Fig. 1478. The same problem has been resolved by Belan-court without employing a parallelogram: two pieces ofwood, ab,do, turn round the points or centres a and o, theirextremities l and d are fixed to each other by the iron piecebed , with articulations at b and d; the lengths ab and do fromcentre to centre of the gudgeons are equal. The sumab + do of these lengths is equal to the distance from thepoint a to the point o measured horizontally, so that whenab and do are level, the right line passing through d and b isvertical; and as the length of the piece bd , from centre tocentre of the gudgeons, is equal to the difference of level of thepoints a and o, bd becomes vertical at the same time thatab and do become horizontal.
Fig. 1479. The drill bow, too well known to require anyexplanation.
Fig. 1480. If we cause a wheel a to turn in any direction,the wheel b will turn in an opposite direction, and both willact in corresponding racks, so as to communicate a rectilinearmotion to the rod cd.
Fig. 1481. is a modification of the preceding, adapted tomany useful applications. If on an axis we fix two toothedwheels, and make two racks diametrically opposite engageeach of these wheels, the circular alternate motion of the axlewill communicate an alternate rectilinear motion to the racks,and the extremities of these same racks will approach orretire from the axle in a uniform manner: it is thus thatreels have been constructed, and that we may form a cylinderwhose diameter shall be variable as that of which we havebefore spoken, by multiplying the number of wheels and racksagreeable thereto.
3 S
Fig. 1475.
Fig. 1177.
Fig. 1478.
Fig. 1479.
Fig. 1480.