Note O — Chapter VI · GENERAL CHARACTERISTICS AND MISCELLANEOUS NOTICES.

The inexperienced mechanic is liable to be puzzled with the action of the wedge, because of its being estimated, in some modes of its application, in the double proportion of its length to that of once its thickness, giving to it, apparently, twice the force of the other mechanical powers. It may not be unfitting, for the sake of our young readers, to explain the little difficulty. The wedge when acting against one fixed and immoveable body for the removal of another body, has then, only, the like force as the lever,—a force proportionate to the extent of space passed over, in driving, by the length, with respect to the increase in the thickness, of the wedge; but when acting for the separation of two bodies, both moveable, both sides then become effective, and it necessarily exerts double that power. And so does the lever. For if the lever be employed in like manner, the action in separating two moveable bodies will be just double that of its ordinary action where the fulcrum is absolutely fixed. This, indeed, is obviously the same with all the mechanical powers. Action and reaction being equal, the power exerted in raising or moving one heavy body must be exerted reversely against the earth, or other fixed body serving as a fulcrum to the lever, or for the attachment of one extremity of a tackle or series of pullies, or for the securing of the capstan spindle. Let the attachments of the machine and its object, however, be both afloat, and then any of the mechanical powers, like that of the wedge, will have an efficiency of double that of its ordinary operation where one part is a fixture.