If the shock is too intense it may be weakened by drawing the carbon and zinc poles partly out of the bichromate solution; or a regulator may be made of a large glass tube and a glass preserving-jar filled with water. If the tube cannot be had, an Argand gas-burner chimney will answer as well. Solder a wire to the edge of a small tin or copper disk, as shown in Fig. 10, on which the chimney rests at the bottom of the jar, and another wire to a tin box-cover with some small holes punched in its top, this latter being suspended within the chimney. This second wire is passed out through a cork at the top of the chimney made of a disk of cardboard and a piece of wood. One wire is connected with A of Fig. 8 and the other with a battery-pole. This apparatus acts the same as a resistance-coil, and by raising or lowering the box-cover the current is increased or diminished. The closer the cover comes to the disk the stronger the current, as there is less water for the electricity to pass through and therefore less resistance; while if the cover touches the disk the current flows as freely as if there were no regulator and the wires ran directly to the cell. An apparatus comprising a coil, an interrupter, or armature, and a switch may be set on one block, and the arrangement of the several parts is clearly shown in the drawing of the complete galvano-faradic apparatus (Fig. 11). The block should be six inches long, four inches wide, and seven-eighths of an inch in thickness. [Illustration: FIG. 8] [Illustration: FIG. 9] [Illustration: FIG. 10] [Illustration: FIG. 11] [Illustration: FIG. 12] The coil is made as described for Fig. 8, the spool being three inches long and one inch and a quarter in diameter. A carriage-bolt three inches and a half long and five-sixteenths of an inch in diameter, with a bevelled head, is made fast in the spool, and this coil is strapped to the block with two metal bands and screws. Two binding-posts (A and B of Fig. 11) are arranged at the upper corners, and to these the ends of the secondary coil wires are attached. Two more binding-posts (C and D of Fig. 11) are arranged at the lower side and provided with a switch to open and close the circuit. One of the primary coil wires is made fast to C, and the other one to a block which contains the set-screw that bears against the vibrating armature. Its arrangement and the wire connection is explained in Fig. 9 B. An armature of thin brass or tin is made and attached to a block (E in Fig. 11). At the loose end that is opposite the bolt-head several wraps of tin are made and soldered fast, or a small block of soft iron may be riveted to the armature. It must be of iron or tin, however, so as to be attracted by the electro-magnetized bolt-head. This arrangement may be seen in Fig. 12. Attach a thick piece of paper over the bolt-head, so that the lug at the end of the armature will not adhere to it through residual magnetism.