[Illustration:  FIG. 4A]

[Illustration:  FIGS. 4, 4B and 4C]

Further, each lamp has its own separate adjustable resistance, fuse, and switch.  These are of special construction, combined in one, and are illustrated in Figs. 4 and 4A; the other figures, 4B and 4C, showing some of the details of the same.  The wires, W W, lead from and to one lamp.  The current enters at one wire, passes through the fuse, f—­Figs. 4C and 4A—­down the center of the cylinder to a divided contact, into which a switch arm can be shot.  When this is so, a connection is made to the upright brass rod, T, which serves to grip the band, R, passing round the body of the cylinder.  The current then passes through all the turns of wire above the band, and out at the other terminal.  The resistance can be varied by raising or lowering the band.  Fig. 4B shows the manner of tightening the band against the wires on the cylinder.  The upright rod, T, is seen in section, and is fixed in one position to the frame of the apparatus.  Abutting against this, and working in the block to which the two ends of the band are screwed, is a thumb screw, S, by turning which the band may be loosened for adjusting, and tightened when the right position is found.  The cylinder is covered with asbestos sheet, and the wire, which is of nickel, and measures altogether from 3 to 4 ohms, is wound helically round this.  The switch arm, to which the handle is attached below, does not itself make and break the circuit, but carries a spring, as shown, which, when the arm is at the end of its movement, pulls over the contact lever with a rapid action, shooting the same between the divided contact piece, and making a perfect contact.  The switchboard forms one side of a closed wooden case or cupboard, with sufficient room for a man to enter and adjust the resistances or switches for each lamp.  These are screwed to the inside of the case in rows, to the number of twenty-five.  The greatest care has been taken in the fixing of the connections to the inside of this case, and no leading wires of different potential are allowed to cross each other.

[Illustration:  FIG. 11A]

The Oerlikon lamp, which is designed to work with constant potential, is shown partly in section in Fig. 8.  There is only one solenoid, A, through which all the current passes, and whose action is to strike the arc and maintain the current constant.  The soft iron core, C, is suspended from the inside of the tube, T, in which it has an up and down movement checked by an air piston in the tube.  An end elevation of the brake wheels and solenoid is given in Fig. 9, where it will be seen that the spindle carrying these wheels also carries between them a pinion engaging with the rack rod, R. The top carbon attached to the rack rod falls by its own weight, and is therefore in contact with the lower carbon before the lamp is switched in circuit.  When this is done the core is instantly magnetized, and attracted to the soft