954

THEORY AND PRACTICE OK ENGINEERING.

Book II.

Fig. 132<>.

Fig. 1327.

slide between the two small bridges p and q, and which has aperpendicular rod ef from one part of which, at a greater orless distance from the rule c d, rises another cylinder, which isinserted, like the first, in the longitudinal groove m of therule ab; but on the opposite side to that on which is thecylinder c, and in such a manner that when the rules are inmotion they do not meet.

If we move the rule so that its point a goes over the lineA G, parallel to the rule C D, the point a will in the same timego over the right line ab. It is thus by the continual rectilineal motion of the point a wecan communicate to the rule d a motion of the same kind with the relative velocity werequire, and even in a contrary direction by placing the cylinder a conveniently in the rode/.

Let A be a wedge which may slide in the direction of itslength between four pillars, whilst another wedge B is retainedby pins, or, what is better for the diminution of friction, byrollers fixed in the same wedge, and which touch the pillars;it is clear if we push the wedge A, B will rise, preserv ing itsparallelism. Supposing the force applied to the wedge A in thedirection of the base a 6, and a rule Ip , perpendicular to theinclined plane ab ; the extremity of this rule has a frictionroller at l, it leans on the inclined plane, and the rule slidesbetween the bridges c,g.

It is evident that, the inclination of the plane being arbitrary,we may transform a continuous rectilinear motion into another, which will form a given anglewith the first; the velocity of the first will be to that of the second, as the radius is to thesine cba. If the angle eba were zero, the rule Ip would rest motionless, which happenswhen rectilinear motion is changed to another also rectilineal, but the direction of which isperpendicular to the first; we obtain this result by means of the second wedge 15, and it weadd a third, C, which forms one body with the second, we may change the direction ot motionat pleasure, as well as the ratio of velocities ; the line cb may have any curvature, and inthis case the continuous rectilinear would be transformed into an alternate rectilinear motion.

Montgolfier s Hydraulic Ram . The current of a river orwaterfall is a mover, acting in a constant rectilinear direction,and communicates alternate motion to a valve; this, secondedby a reservoir of air, causes a continuous flowing of water,which may be regarded as a continuous rectilinear motion.

This machine, first constructed in 1797, has been broughtto very great perfection since, and in some cases usefully em-ployed. The large pipe, which is called the body of the ram,passes through the side of the reservoir, from which the fall ofwater is obtained ; this pipe generally is formed with a trum-pet mouth at one end, and at the other the opening canbe closed by valves, through which, when open, the waterissues with a velocity dependent upon the height at which itstands in the reservoir from whence the supply is drawn.

The valve is made of metal, with a hollow cup or dish attachedto its lower surface, and its seat is made a little wider than the diameter of the pipe, whichconsists of a short cylinder screwed bv a flanch into the upper surface of the ram ; thiscylinder is so formed as to have an inverted cap or annular space round the upper, forcontaining air, which cannot escape when it is compressed by tbe water. From tins annularspace there is a small pipe, communicating with the open air, furnished with valves, one ofwhich opens inwards to admit air, and prevent its return, whilst the other admits a certainquantity of air, and then shuts and prevents any further entrance. When these valves areopened by hydrostatic pressure, a portion of the water flows into the air-vessel, and con-denses the air it contains, and the water in it is thrown to a height sufficient to balancethe elasticity of the air shut up in the chamber.

Continuous rectilinear motion with a uniform velocity, or which variesaccording to a given law, may be changed into alternate rectilinear motion,with a velocity of the same nature as that of the movement which produces it,constant or variable according to a given law, in the same or in different planes.

This machine consists of two cylindrical pipes a and b, whose axes arein the same vertical direction ; they are separated from each other byan interval dependent on a condition we are about to indicate.

The upper extremity of the pipe a is closed by a plate in which ispierced a circular orifice answering to that in the pipe b. C is a circulardiaphragm whose diameter is smaller than that of the orifice dd,a little below which it is placed.

Fig. 1328.

l'ig. 1320.