492 KINEMATICS OF MACHINERY.
is obviously a mere accidental condition, and there is no difficulty in supposing a locomotive built like a Faiiiie engine on a frame sufficiently long to afford ample room for both. No part corre- sponding to the tool can, however, be pointed out ; it is only certain that the couplings can no longer in any way represent it. The body to be acted upon, indeed, no longer exists beside or outside the machine, but has become a part of it. The one frame supports both carriage and machine.
There are many other machines in which the conditions are ex- actly the same as in the locomotive, as, for example, the steam- boat ; where again we can find nothing corresponding to the tool. In small machines we find the same thing ; it is very difficult to say, for instance, what part of the common clock is the tool. If it be the hands, we ask immediately where the body is upon which the hands work. The hands also are not absolutely necessary to the completeness of the clock ; they might be replaced by graduated discs turning relatively to some fixed index ; or indeed a mere mark made upon a wheel exposed to view might answer all purposes. The hands therefore are not the tool, and it is not possible to name any other part of the clock which fulfils the functions of that organ.
Our investigation thus leads us to the conclusion that the tool does not form an essential part of the machine. In certain machines only do we find it unmistakably recognisable, in some its distinctness is less and in others it does not exist at all.
Looking at the last class of machines of which we have given examples in the crane, locomotive, steam-boat and clock collect- ively, we find that they have in common the object of effecting some alteration in the position of a body or bodies. The first three examples are machines by which loads are moved, vertically, hori- zontally, or in both directions. Essentially the same thing is true of the clock, but here, for a special purpose, the alterations of position are so arranged that they enable us to measure the time occupied by the process.
The machines first considered, in which the tool really exists, have, on the other hand, the common object of making some alter- ation in the form of the body or bodies upon which work is done such as turning, grinding, dividing, uniting, etc., Lathe, planing-machine, screwing-machine and saw change the form of
