328 MARIENFELDE-ZOSSEN ELECTRIC-RAILWAY TRIALS. 



slipped over the car axle, on which the armature of the motor is built. 

 The motor is coupled to the wheels of the corresponding axle by means 

 of doul)le arms attached on both ends of the hollow axle and touching 

 the sliding pieces placed on the wheels. The weight of the motor, 

 instead of resting immediately on the axles of the car, is thus sup- 

 ported ])y bearing springs on the axle boxes of the truck. 



The motors constructed by the Siemens & llalske Company on the 

 other hand are ()-pole motors, also for outputs of 250 horsepower each, 

 the energy current being conve3'ed to the rotor at a tension of 1,150 

 volts b}' means of three sliding rings. The pressure in the secondary 

 circuit at rest and at first starting is 650 volts. The rotor is provided 

 with closed direct-current bar windings, whereas the stationary part 

 of the motor has rotary-current bar windings. The rotor with its box 

 is pressed strongl}^ on the axle of the car. The stationary part of the 

 motor, inclosed by a double cast-iron casing, rests without any inter- 

 mediate spring on the car-axle bearings. The diameter of the rotor is 

 7<S0 millimeters, whereas the external diameter of the motoi' is 1,050 

 millimeters. 



Both the direct fixing of the motors on the axles and the suspension 

 by springs on the truck have giv^en full satisfaction in connection with 

 the experiments so far made. In general, the spring suspension seems 

 to be preferable to the rigid suspension of the motor. 



J-Cxeiters and resit^tanees.— The. exciters and resistances, necessary in 

 starting and in controlling the speed, show also some essential difier- 

 ences in the two carriages. In order to avoid any. abrupt variations 

 in the speed and any excessive sparking in the car,* the resistances must 

 be switched off from the circuit quite gradually. In the Allgemeine 

 Elektrizitats Gesellschaft car there are to this efi'ect liquid resistances 

 of the following construction: 



The terminal plates of the opened circuits are placed in two reser- 

 voirs in th(; central machine room of the car. Beside each of the 

 reservoirs thei-e is an electrically driven centrifugal ])ump, conveying 

 into the upper reservoir a soda solution placed in a ])()x l)elow the 

 carriage. The higher the liquid in the latter the smaller will bo the 

 resistance ])etween the electrodes. The height of the licjuid is regulated 

 from the driver's cab l)y means of a valve. The pumps work perma- 

 nentl}^ during the run, the liquid circulating in a tube conduit insui-ing 

 a permanent cooling (rcfi-igei'ation). This excitei- afloi'ds the advan- 

 tage of dispensing with the contacis and cable joints necessary in con- 

 nection with solid exciters. 



In the Siemens & llalske car, on the other hand, there are metallic 

 resistances, formed of "Kruppine'"* bands 45 ))y 2 millimeters in section. 

 These bands are placed by groups in flat boxes fitted outside on the 

 lotigitudinal wall of the car, below the window. There are in all 29 

 steps, four being intended for the Hrst inserting and 25 for increasing 



