9G0
THEORY AXD PRACTICE OF ENGINEERING.
Book II.
Fig. 1345.
Continuous rectilinear motion with a uniform velocity, or varying according to a given law,may be changed into circular alternate motion with a velocity of thesame nature as that of the motion which produces it, in the same pi meor in different planes. Fig. 13*45. represents a method invented l»vPerrault of applying a fall of water to the movement of a clock :the water which flows through c falls into a small chest e,which turns round an axis a, and is divided by a partition into twoparts : when the base is horizontal the water flows in such amanner as to be divided into two equal parts; by the partition inany other position the fall is into the elevated part; in that repre-sented by the figure the fall takes place in the side ej when thispart is full, the chest turns on its axis and leans on the obstacler, emptying the water whose weight has decided its motion ; theother part is filled in its turn, and restores the chest to its primi-tive position.
Continuous rectilinear motion is converted into circular motionby means of a descending weight attached to a cord wound on anaxle, as we have already described: but to convert a reciprocatingrectilinear motion into a continuous circular for a long time baffled the skill of ourmechanics; it is, however, now generally effected by means of a cranh applied in threedifferent manners : first, where the moving force may be uniform, and in a straight line;second, where the moving force may be uniform, and in a curved line ; and, thirdly, wherein either case the force may be variable. A crank increases also the velocity of the movingforce in the usual construction, in the ratio of the circumference of a circle to twice its dia-meter ; but this ratio, as well as the action of the power, varies : for the crank motion whichconverted the reciprocating motion of a piston rod into a rotaryone, a patent was granted in 1769, 1778, and 1781; that invented bySteed was the most simple. Mr. "Watt in 1781 obtained a patentfor five other kinds of crank, one of which was the sun-and-planet-wheel motion, which he applied to his expansive steam-engines: the “ Annals of Science” show how great was the diffi-culty of converting a reciprocating rectilinear motion into acircular one, and by what patient investigation and labour it wasovercome.
To transform circular alternate into continuous rectilinear. — Letac be a lever turning on its axis e ; rr a bar which may ascendand descend freely, and whose edges are ratchet-toothed ; dn, dnare two small levers turning on their axes d, d, and whose ex-tremities n and n are furnished with small cylinders, which engagethe teeth of the bar ; the circular alternate motion of the lever cwill cause the bar to mount.
A boat at anchor in the middle of a river attached to a cablesufficiently long will go from one bank to the other with acircular alternate motion by means of its rudder, a method oftenemployed in crossing a ferry.
A sector surmounted by a sail whose centre of gravity is very **8*1347.much below that of oscillation, by means of a counterpoise, con-tinually balances itself with a circular alternate motion, when thewind strikes the sail. This method of applying the action of thewind has often been proposed, and models on this principle arefound at Paris.
Continuous rectilinear motion with a uniform velocity, or which variesaccording to a given law, may be changed into continuous in a givencurve, with a velocity of the same nature as that of the motion whichpro<luces it, constant or variable according to a given law , in the sameplane or in different planes.
Rectilinear continuous motion with a uniform velocity , or whichvaries according to a given lau\ may be changed into alternate in agiven curve with a velocity of the same nature as that of the motion whichproduces it, constant or variable according to a given law, in thesame plane or in different planes.
Continuous rectilinear motion may be changed into continuous circularby the means before indicated.
Circular continuous motion, with a uniform velocity, or which varies according to a givenlaw, may be changed into alternate rectilinear, with the velocity of the same nature with that ofthe motion which produces it; constant or variable , according to a given law, in the same planeor in different planes.