e number
lamp is burning. The classification lamp, lubricator and order or
reading lamp, are controlled by a small switch on the socket of each
lamp.

51. Q. For what purpose is the dimmer, and how does it operate?

A. It is to reduce the intensity of the headlight when locomotive is in
yards or around stations. It consists of a small resistance tube in the
wiring circuit, and with the cab switch in dimmer position, a portion of
the current is converted into heat instead of light.

52. Q. How is an incandescent headlight focussed?

A. By moving the lamp in its position in the reflector until the most
brilliant and compact beam of light is obtained. If the beam does not
strike the track centrally, or as high or low, the headlight case must
be moved on its platform until the beam is properly directed. It is
often necessary to raise the front or back of the case by shimming
between the case and its platform in order to direct the beam of light
the proper distance ahead of the locomotive.

53. Q. What provision is made for moving or focussing the lamp in the
reflector?

A. When the lamp is mounted horizontally there are thumb screws by which
the lamp may be moved sidewise, up and down, and forward and backward.
This mounting is called the "micrometer" device, because of the accuracy
of adjustment. With the vertical mounting, a flat head thumb screw at
the base of the lamp support releases the ball joint so that the lamp
may be easily moved sidewise or forward and backward. To raise or lower
the lamp, the thumb screw higher on the lamp stand must be loosened.

54. Q. What causes a "black spot" in the illumination ahead of the
locomotive?

A. The lamp is out of focus, being too far ahead or back of the proper
position in the reflector.

55. Q. How would you remedy the following possible defects?

A. (a) =All lamps fail to burn.= If turbine is not running the wrong
steam valve in the cab may have been opened, or there may be a second
valve, closed, in the steam pipe. The screen on the governor valve in
the turbine may be clogged. Remove brass cap at top of turbine and
unscrew screen or strainer-cap.

(b) =Turbo-generator runs, but no lights.= Wires may be
"short-circuited" (crossed) which will cause brushes to spark badly, and
turbo-generator to pull hard. The "short" can usually be found by an
occasional sparking or smoke at the point of trouble. Separate and
protect wires when short is found. The brushes may be