are of fireproof composite, faced with aluminum sheets.  The mouldings throughout are of aluminum.  The wainscoting is of “transite” board and aluminum, and the end finish and window panels are of aluminum, lined with asbestos felt.  The seat frames are of steel throughout, as are also the cushion frames.  The sash is double, the lower part being stationary and the upper part movable.  The doors are of mahogany, and are of the sliding type and are operated by the door operating device already described.

[Illustration:  SIDE VIEW OF MOTOR TRUCK]

[Sidenote:  Trucks]

Two types of trucks are being built, one for the motor end, the other for the trailer end of the car.  The following are the principal dimensions of the trucks: 

Motor Truck.  Trailer Truck.

Gauge of track,.............................   4’ 8-1/2”         4’ 8-1/2”
Distance between backs of wheel flanges,....   4’ 5-3/8”         4’ 5-3/8”
Height of truck center plate above rail,
car body loaded with 15,000 pounds,.......         30”               30”
Height of truck side bearings above rail,
car body loaded,..........................         34”               34”
Wheel base of truck,........................       6’ 8”             5’ 6”
Weight on center plate with car body
loaded, about............................. 27,000 lbs. 
Side frames, wrought-iron forged,........... 2-1/2” x 4”       1-1/2” x 3”
Pedestals, wrought-iron forged,......................... 
Center transom, steel channel,.......................... 
Truck bolster,.............................. cast steel.    wood and iron. 
Equalizing bars, wrought iron,.......................... 
Center plate, cast steel,............................... 
Spring plank, wrought iron,.................     1” x 3”        white oak. 
Bolster springs, elliptic, length, .........         30”               32”
Equalizing springs, double coil,
outside dimensions,................... 4-7/8” x 7-1/2”       3-5/8” x 6”
Wheels, cast steel spoke center,
steel tired, diameter,....................     33-3/4”               30”
Tires, tread M. C. B. Standard,......... 2-5/8” x 5-1/4”   2-5/8” x 5-1/4”
Axles, diameter at center,..................      6-1/2”            4-3/4”
Axles, diameter at gear seat,...............    7-13/16”
Axles, diameter at wheel seat,..............      7-3/4”            5-3/4”
Journals,...................................     5” x 9”       4-1/4” x 8”
Journal boxes, malleable iron,
M. C. B. Standard,....................................

Both the motor and the trailer trucks have been designed with the greatest care for severe service, and their details are the outcome of years of practical experience.

CHAPTER IX

SIGNAL SYSTEM