Author Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1883 edition. Excerpt:...and be made quicker or slower at pleasure. The curve will evidently be somewhat similar to the continuous Indicator diagram (Plate I. Fig. 2), consisting of a series of undulations according to the force of the steam and its action on the propeller. A zero-line must be got, as in the case of the Indicator. When the Dynamometer is applied to large engines, the levers can be relieved of the pressure of the shaft; and this being accomplished, the index of the spring-balance will stand at 0, when the zero-line may be traced. The balance will also give the scale of pounds. After the diagram is traced, draw a series of equidistant lines at right angles to the zero-line, as in Plate I. Fig. 4, which represents a Dynamometer diagram taken on board Rattler during her trial with Alecto, the dimensions being reduced one-half. The distance between the curve and zero-line must be measured and compared with the scale of pounds on the balance. Let this be registered on the diagram in its proper space. These must be added up, and the sum be divided by the number of spaces taken into account. Thus we shall obtain the mean force of the lever on the spring of the balance; let this be multiplied again by the leverage of the Dynamometer, and the result will be the pressure of the screwshaft on the Dynamometer, and therefore on the vessel. To obtain the leverage, if the lever be compound, multiply together all the long arms (measuring from the fulcrum), A doubt has been expressed by some whether this is really the force exerted by the shaft on the vessel, on account of the shaft acting on a lever that yields to its force; but independently of the fact, that none of the thrust can be lost, it is clear that the thrust at C is equal to the thrust at D and that at...