MULTIPLEX TELEPHONY AND TELEGRAPHY SQUIEK. 135 



Electric waves of ultra sound frequencies are guided by means of 

 wires of an existing commercial installation and are made tlie vehicle 

 for the transmission of additional telephonic and telegraphic messages. 



APPARATUS AND EQUIPMENT. 



Under a special appropriation granted to the Signal Corps by Con- 

 gress in the army appropriation act of 1909, a small research labora- 

 tory has been established at the Bureau of Standards, in the suburbs 

 of the city of Washington. This laboratory is equipped with the 

 latest forms of apparatus now employed in the wireless telephone and 

 telegraph art, and also with the standard types of telephone and 

 telegraph apparatus now used upon wire circuits. The small con- 

 struction laboratory of the United States Signal Corps is located at 

 1710 Pennsylvanue Avenue and is also equipped with the usual types 

 and forms of apparatus used in transmitting intelligence by electrical 

 means. Each of these laboratories is supplied with a wireless tele- 

 phone and telegraph installation with suitable antennae. In addi- 

 tion, these two laboratories are connected by a standard telephone 

 cable line about 7 miles in length, which was employed in the experi- 

 ments described below. 



THE 100,000-CYCLE GENERATOR. 1 



The high-frequency alternator, which is shown complete with 

 driving motor and switchboard in the accompanying illustrations, is 

 a special form of the inductor type designed for a frequency of 100,000 

 cycles with an output of 2 kilowatts, making it adapted for use in 

 wireless telephony or telegraphy (pi. 1). 



Driving motor. — The motor is a shunt- wound 10-horsepower ma- 

 chine with a normal speed of 1,250 revolutions per minute. It is 

 connected by a chain drive to an intermediate shaft which runs at a 

 speed of 2,000 revolutions per minute. The intermediate shaft 

 drives the flexible shaft of the alternator through a De Laval turbine 

 gearing, having a ratio of 10 to 1. The flexible shaft and inductor 

 thus revolve at a speed of 20,000 revolutions per minute. 



Field coils. — The field coils, mounted on the stationary iron frame 

 of the alternator, surround the periphery of the inductor. The 

 magnetic flux produced by these coils passes through the laminated 

 armature and armature coils, the air gap, and the inductor. This 

 flux is periodically decreased by the nonmagnetic sections of phos- 

 phor-bronze embedded radially in the inductor at its periphery. 



Armature coils. — The armature or stators are ring-shaped and are 

 made of laminated iron. Six hundred slots are cut on the radial 

 face of each; a quadruple silk-covered copper wire, 0.016 inch (0.4 



i Alexanderson, Trans. Amer. Inst. Electr. Eng., vol. 28, p. 399, 1909. 



