Page:The Kinematics of Machinery.djvu/608

 otherwise have acted." Any tool whatever; a needle, a pencil, &c., is therefore by itself a machine.

. "The industrial .... machines have for their purpose the performing of certain work by the help of motors or moving forces provided for us by nature." An explanation full of restrictions, which gives us only one of the purposes of the machine.

. "A machine is a tool of which the general purpose is the transference of a force from its point of application to a position where it can act so as to overcome a resistance, and execute work which it would be difficult, and sometimes impossible for the same force to execute if applied directly." What then is a "tool?" And how does "sometimes" find its way into a scientific definition?

. Geostatik, 3rd Edit, 1860. "By the name machine, we indicate a combination of rigid bodies, inoveable and immoveable, into a rigid unalterable 'free' (lose) system, by means of which forces, through changes in their direction and magnitude, may be made to balance each other." He has explained in an earlier part of the work what a "free" system is. According to this definition, a suspended iron chain would be a machine; an hydraulic press, however, could not receive that name, for the water is not a rigid body.

. Geostatik, 2nd Edit., 1845. Almost exactly as Weisbach.

. Allgemeine Maschinenlehre, i. (1862). "The machine is a combination of moveable and immoveable rigid bodies which serves to receive physical forces and to transmit them, changing if required their direction and magnitude, in a manner suitable for the performance of definite mechanical work." Here are three definitions coming to us from the same pen: to which shall we trust?

. "Machines are arrangements which transmit the action of forces in order to balance or to overcome other forces, and to produce motions for definite purposes." This covers, e.g., the tow-line of a ship.

. "A machine is an arrangement for the alteration of a given force." Very concise, but somewhat difficult to understand. What is it to "alter a given force"?

. "A machine is a combination of bodies, of which the purpose is the accomplishment of any work by some disposable force." The first few words sound like a definition, the conclusion, however, becomes altogether indefinite.

. "By machines, we mean those artificial arrangements by which motions may with advantage be produced, prevented, or transmitted in definite directions." What has "advantage" to do with science? Motions also cannot be produced by "arrangements;" and so on.

. (Analytische Mechanik, 1868.) "A machine is an apparatus which serves to transmit mechanical energy, or also, to make a force to act at a point which does not lie in its own direction." Again, only characteristics, no explanation, no rigid definition; and that fatal "or also!"

. "An instrument, by means of which we may produce any between two pieces." We might call this definition an equation with two unknowns.