I will, therefore, describe one of the simplest forms of these machines, such as any one, with a little care and patience, can make for himself.
The first thing to do is to get a general idea of what you are going to construct, which may be had from the illustration, and from the actual machines you may sometimes see in a shop window or in a scientific collection, like the Science Departments of the South Kensington Museum. It is the making of the cylinder machine we are going to work out, and, therefore, to begin with, the glass cylinder must be procured. This can be had from a dealer in chemical apparatus and costs only a few pence for the smaller size--about 3 inches by 6 inches. At the same time purchase a round glass rod, 3/8 inch diameter by 5 inches long; a sheet or two of tinfoil, and sixpennyworth of amalgam. From a carpenter or timber-merchant you will require a base-board for the machine, say 13 inches by 8 inches, by 1 inch thick, and of heavy wood; also two uprights, which are to stand on the base-board to support the cylinder. These may be 6 inches tall, by 2 inches by 3/4 inch.
Having now the principal parts of the frame, the work of fitting together can be begun by making a circular hole (centre about 1-1/4 inches from the end) in one wooden upright, to take easily one of the projecting glass pieces, or pivots, at the ends of the cylinder--probably 3/4 inch diameter will do. This hole may be made with a brace and suitable bit, or failing that, with a round chisel--taking care not to split the wood. In one end of the other upright cut a slot of same width as the hole, the bottoms of both being on the same level. Then rest the two glass pivots in the hole and slot, holding the uprights vertically on the base-board, when the cylinder should be quite horizontal. If it is not so, deepen the slot, or shorten either upright, as required. Drill a hole through the two sides of the slot at the top, and insert a round nail to keep the pivot from having too much play.
It will next be necessary to secure these supports to the board, which may be done by driving stout screws from below, together with the aid of some strong glue. If you have the skill it will be better to sink the supports 1/2 inch into the surface.