Finding the number of wood-cuts necessary to explain the parts of the Calculating Engine considerable, and the expense great, it appeared to me that the method of copying by casting might, perhaps, be employed for the purpose of diminishing the evil.

The plan which occurred to me was, to make a drawing of that portion of the mechanism required to be explained, which should contain every part necessary for its action, and, in some cases, even the framework requisite for its support. Such a drawing would be far too complicated for the ordinary reader, and might appear confusion even to the contriver of the machine. This drawing was then to be sent to the wood-cutter to be engraved, and on its return, it was to be sent to the stereotype founder, for the purpose of having any number of fac-similes made in type-metal. Now, each of these plates would, like the original wood-cut, express the drawing in relief, and, by cutting away any line in the plate, that line would be removed in the impression.

The first thing to be done was, to remove from one of these stereotype plates every line, except those which formed the framing of the mechanism. The next step was, to remove from another of those plates all the framing, and every other line, except those which represented two or three of the principal wheels and levers.