A.—­Yes, many plans,—­some of them displaying much ingenuity, but all displaying a complete ignorance of the first principles of mechanics, which teach that power cannot be gained by any multiplication of levers and wheels.  I have occasionally heard persons say:  “You gain a great deal of power by the use of a capstan; why not apply the same resource in the case of a steam vessel, and increase the power of your engine by placing a capstan motion between the engine and paddle wheels?” Others I have heard say:  “By the hydraulic press you can obtain unlimited power; why not then interpose a hydraulic press between the engines and the paddles?” To these questions the reply is sufficiently obvious.  Whatever you gain in force you lose in velocity; and it would benefit you little to make the paddles revolve with ten times the force, if you at the same time caused them to make only a tenth of the number of revolutions.  You cannot, by any combination of mechanism, get increased force and increased speed at the same time, or increased force without diminished speed; and it is from the ignorance of this inexorable condition, that such myriads of schemes for the realization of perpetual motion, by combinations of levers, weights, wheels, quicksilver, cranks, and other mere pieces of inert matter, have been propounded.

49. Q.—­Then a force once called into existence cannot be destroyed?

A.—­No; force is eternal, if by force you mean power, or in other words pressure acting though space.  But if by force you mean mere pressure, then it furnishes no measure of power.  Power is not measurable by force but by force and velocity combined.

50. Q.—­Is not power lost when two moving bodies strike one other and come to a state of rest?

A.—­No, not even then.  The bodies if elastic will rebound from one another with their original velocity; if not elastic they will sustain an alteration of form, and heat or electricity will be generated of equivalent value to the power which has disappeared.

51. Q.—­Then if mechanical power cannot be lost, and is being daily called into existence, must not there be a daily increase in the power existing in the world?

A.—­That appears probable unless it flows back in the shape of heat or electricity to the celestial spaces.  The source of mechanical power is the sun which exhales vapors that descend in rain, to turn mills, or which causes winds to blow by the unequal rarefaction of the atmosphere.  It is from the sun too that the power comes which is liberated in a steam engine.  The solar rays enable plants to decompose carbonic acid gas, the product of combustion, and the vegetation thus rendered possible is the source of coal and other combustible bodies.  The combustion of coal under a steam boiler therefore merely liberates the power which the sun gave out thousands of years before.

FRICTION.