Chap. XIII.

DYNANOMETER.

1067

Another kind of Spring Balance —The spring of this balance is bent in a curve C K D ,terminated by two braces, C B, DE, one of which supports the pinion I, and the othera rack DEG II, of which the toothed portion G II catches the pinion I. This pinion andthe needle which marks the tension of the spring turn on the same axis.

The face is a circle whosecentre is on the axis of thepinion I, and is fixed by twoscrews t and t\ on the planeTV, which is soldered to theupper brace A B, which carriesthe pinion. To graduate thescale, suspend the balance bythe ring A, and attach knownweights to F by the hook 5 c.

The rack G II will work thepinion I, and the needle fixedon the axis of this pinion takesup successively the positionsfigured from 0 to 100; thesenumbers express the force oftension on the spring in pounds.

The index of the needle de-scribes about g of the inch asthe maximum tension of thespring, or for the greatest dis-tance between the extremitiesC and D of the spring, whichis about 1 *1 inch.

The plane of the balancebeing supposed vertical, asin the projection, on anothervertical plane passing throughthe axis of the pinion; theface of the brace A B, per-pendicular to the plane ofthe limb, is drawn parallelto itself in A' B'; we see onthis face in the parallelogram1 2 3 4, the projection of anopening made in the thickness of the brace A B, to make way for the toothed part GHof the rack; the breadth, 1 2 or 3 4, of this opening is 4 inches; EM is the projection ofthe axis of the pinion I; the spring C K D is projected in C D ; the plane on which theface is screwed has for its projection TV. *1110 spring is *11 of an inch thick, and 1*2inches broad. To render this balance more convenient, a needle is added, which turnsfreely on the face roundthe axis of the pinion I,and may be employed asthe dynanometer; it iseven preferable for mea-suring the ordinarystrength of men.

Of the dynanometricMachi?ie, and the Mea-surement of the tangentialForce of an Axfetree . —

Let A 13, fig. 1636., bethe section of an axlemoved by water or anyother power; an un-known but constant re-sistance acts tangentiallyto this axle, and we re-quire to measure it. Toresolve this question,suppose we fix on theaxle A B of a wheelB E F G H, of any num-

Fig. 1635.

Fig.1636.