MACHINE, in general, whatever hath force sufficient to raise or stop the motion_ of a heavy body.
Machines are either simple or com pound: the simple ones are the seven mechanical powers, viz. lever, balance, gully, axis and wheel, wedge, screw, and inclined plane.
From these the compound ones are formed by various combinations, and serve for different purposes ; in all which, the same general laws take place, viz. that the power and weight sustain each other, when they are in the inverse proportion of the velocities they would have in the directions wherein they act, if they were put in motion. Now, to apply this law to any compound machine, there are four things to be considered : 1. The moving power, or the force that puts the machine in motion ; which may be either men or other animals, weights, springs, the wind, a stream of water, &c. 2. The velocity of this power, or the space it moves over in a given time. 3. The resistance, or quantity of the weight to be moved. 4. The velocity of this weight, or the space it moves over in the same given time.
The two first of these quantities are al ways in the reciprocal proportion of the two last : that is, the product of the first two must always be equal to that of the last : hence, three of these quantities being given, it is easy to find the fourth ; for example, if the quantity of the power be 4, its velocity 15, and the velocity of the weight 2, then the resistance, or quan tity of the weight, will be equal to 4 x —2 15 60 —30.
2 Compound machines are extremely nu merous, as mills, pumps, wheel-carriages, fire-engines, &c. See ENGINE, MILL, PUMP, WATER.WOPICS, &C.
Machine denotes any thing that serves ' to augment or regulate moving powers, or it is a body designed to produce mo tion, so as to save either time or force. Machines are either simple or compound. The simple machilies are the mechanical powers, viz. the lever, the wheel and axis, the pulley, the inclined plane, the Wedge, and the screw. See MECHANICS: These simple machines serve for dif ferent purposes, and it is the business of the skilful mechanician to select and corn bine them in such a manner, as may be best adapted to produce the effect of which he stands in need. Compound machines are formed from these simple ones. These may be indefinitely varied, and they belong to all the branches of science. Descriptions of many of the most useful, and which serve to exhibit the principles of machinery, will be found in various parts of our work. See