The general principle on which this machinery operates, in doing its work, may perhaps be made intelligible to the reader by description. The action is regulated by what are called _patterns_. These patterns are models in iron of the various surfaces of the stock which it is intended to form. Let us suppose, for example, that the large cavity intended to receive the lock is to be cut. The stock on which the operation is to be performed is placed in its bed in the machine, and over it, pendant from a certain movable frame-work of polished steel above, is the cutting tool, a sort of bit or borer, which is to do the work. This borer is made to revolve with immense velocity, and is at the same time susceptible of various other motions at the pleasure of the workman. It may be brought down upon the work, and moved there from side to side, so as to cut out a cavity of any required shape; and such is the mechanism of the machine that these vertical and lateral motions may be made very freely without at all interfering with the swift rotation on which the cutting power of the tool depends. This is effected by causing the tool to revolve by means of small machinery within its frame, while the frame and all within it moves together in the vertical and lateral motions. Now if this were all, it is plain that the cutting of the cavity in the stock would depend upon the action of the workman, and the form given to it would be determined by the manner in which he should guide the tool in its lateral motions, and by the depth to which he should depress it. But this is not all. At a little distance from the cutter, and parallel to it is another descending rod, which is called the guide; and this guide is so connected with the cutting tool, by means of a very complicated and ingenious machinery, that the latter is governed rigidly and exactly in all its movements by the motion of the former. Now there is placed immediately beneath the guide, what is called the pattern, that is a cavity in a block of iron of precisely the form and size which it is intended to give to the cavity in the wooden stock. All that the workman has to do therefore, when the machine is put in motion is to bring the guide down into the pattern and move it about the circumference and through the centre of it. The cutting tool imitating precisely the motions of the guide, enters the wood, and cutting its way in the most perfect manner and with incredible rapidity, forms an exact duplicate of the cavity in the pattern. The theory of this operation is sufficiently curious and striking--but the wonder excited by it is infinitely enhanced by seeing the work done. It is on this principle substantially that all the machines of the Stocking Shop are constructed; every separate recess, perforation, or groove of the piece requiring of course its own separate mechanism. The stocks are passed from one of these engines to another in rapid succession, and come out at last, each one