But while it is not easy by attention to complexity of structure always to distinguish a tool from a machine, nothing is gained by making the differentia of a machine to consist in the use of a steam or other non-human motor.
A vast amount of modern machinery is of course directed not to combining tools or series of productive processes upon which the productive skill of man is closely engaged, but to substituting other motors for the muscular power of man. But though certain tools as well as certain forms of human effort are here replaced by machines, these tools are not commonly embodied in the machinery for generating and transmitting the new force, so that the mere consideration of the different part played by the worker in generating productive force does not assist us to distinguish a machine from a tool. A type-writer, a piano, which receive their impulse from the human muscles, must evidently be included among machines. It is indeed true that these, like others of the same order, are exceptional machines, not merely in that the motive power is derived more essentially from human muscles, but in that the _raison d'être_ of the mechanism has been to provide scope for human skill and not to destroy it. But though it is true that a high degree of skill may be imparted to the first process of the working of a piano or type-writer, it is none the less true that the "tool," the implement which strikes the sound or makes the written mark, is not under immediate control of human touch. The skill is confined to an early process, and the mechanism as a whole must be classed under machinery. Nothing would indeed be gained in logical distinctness if we were to abandon our earlier differentia of the machine and confine that term to such mechanical appliances as derived their power from non-human sources--the fact which commonly marks off modern from earlier forms of machine production. For we should find that this substitution of non-human for human power was also a matter of degree, and that the most complex steam-driven machinery of to-day cannot entirely dispense with some directing impulse of human muscular activity, such as the shovelling of coal into a furnace, though the tendency is ever to reduce the human effort to a minimum in the attainment of a given output.