Volume 183001

Mechanics / By Henry Kater and Dionysius Lardner.

  • Henry Kater
Date:
1830
Catalogue details

Licence: Public Domain Mark

Credit: Mechanics / By Henry Kater and Dionysius Lardner. Source: Wellcome Collection.

    191/408 page 165
    dicular to the surface, and supported by its resistance; the other is parallel to the surface, and supported by the power. The proportion, therefore, of the power to the weight will always depend on the obliquity of the surface to the direction of the weight. This will be easily un- derstood by referring to what has been already explained in Chapter vii. Under this class of machines come the inclined plane, commonly so called, the wedge, the screw, and various others. (232.) In order to simplify the development of the elementary theory of machines, it is expedient to omit the consideration of many circumstances, of which, how- ever, a strict account must be taken before any practically useful application of that theory can be attempted. A machine, as we must for the present contemplate it, is a thing which can have no real or practical existence. Its various parts are considered to be free from friction: all surfaces which move in contact are supposed to be infi- nitely smooth and polished. The solid parts are con- ceived to be absolutely inflexible. The weight and in- ertia of the machine itself are wholly neglected, and we reason upon it as if it were divested of these qualities. Cords and ropes are supposed to have no stiffness, to be in~ finitely flexible. The machine, when it moves, is supposed to suffer no resistance from the atmosphere, and to be in all respects circumstanced as if it were in vacuo. It is scarcely necessary to state, that, all these suppo- sitions being false, none of the consequences deduced from them can be true. Nevertheless, as it is the business of art to bring machines as near to this state of ideal perfection as possible, the conclusions which are thus obtained, though false in a strict sense, yet deviate from the truth in but a small degree. Like the first outline of a picture, they resemble in their general features that truth to which, after many subsequent corrections, they must finally approximate. After a first approximation has been made on the several false suppositions which have been mentioned, M 3
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