From white-wood, half an inch thick, cut two blocks three inches and a quarter square. In one of them (the rear one) bore a hole at the centre, of such size that a piece of three-eighth-inch gas-pipe can be screwed into it. In the other one make a hole two inches in diameter, so that the cover of a small tin can will fit into it. Outside this hole, and on one side of the block, cut the wood away and down for one-eighth of an inch, forming a rabbet, as shown at A in Fig. 7. This will be the back of the front block. [Illustration: FIG. 7 AN ELECTRIC HORN] Have a gas or steam fitter cut a piece of two-inch iron pipe one inch and three-quarters long. This will measure a trifle over two inches and a quarter, outside diameter, and will form the cylinder or cover for the mechanism. The piece of pipe should fit snugly in the front board, and at the rear one the wood should be cut away so as to let it in an eighth of an inch, as shown in the sectional plan of Fig. 7. Obtain a piece of three-eighth-inch gas-pipe, threaded at one end. Cut it with a hack-saw, and file the blunt end so that it will measure one inch and seven-eighths long, as shown at C in Fig. 7. This is to be screwed into the front of the rear block so that it will project one inch and a half. Make a spool to fit the pipe, as shown at B in Fig. 7, or use two wooden button-moulds attached to the pipe with shellac or glue. Between them wind on the coils of No. 22 wire to form the helix. Cut a hole in the tin-can cover, as shown at D in Fig. 7, and have a tinsmith solder a small funnel to it (for the horn, or bell, as it is called), cutting away the lower part of the funnel so that the hole in it will correspond in size with that in the can cover. This joint can be made at home by fitting the funnel in the hole and then turning back the edge, as shown in the sectional drawing at E in Fig. 7. Then, with a spirit-lamp, some soldering solution, and solder, make a good joint. Small holes are to be made at the corners of the blocks, through which stove-bolts two inches and a half long will fit to bind the front, back, and cylinder together.