252 BELL SYSTEM TECHNICAL JOURNAL 



A commutator and relays associated with the pneumatic apparatus 

 serve to equaUze the lengths of the transmitted signals and to provide 

 any desired ratio of "marking" to "spacing." This transmitter is 

 capable of operating at speeds up to about 2500 letters per minute. 



The high-speed siphon recorder is shown in Fig. 9. It differs from 

 the standard instrument in many respects. A very light moving 

 coil is supported horizontally in the strong field of an electromagnet 

 by a bifilar suspension. A very light rigid arm attached to the coil 

 carries a siphon pen only about 2 cm. long which writes on ordinary 



Fig. 9 — High-speed siphon recorder 



recorder tape drawn rapidly over a vertical table. This instrument 

 may also be operated at 2500 letters per minute with cable-code and 

 makes a record similar to that of the standard siphon recorder. 



Both of these instruments and the signal-shaping amplifier were 

 provided in advance of laying the first permalloy-loaded cable and 

 were used on the first tests. A record of an early test message made 

 on the New York-Horta cable at a speed of 1920 letters per minute is 

 shown in Fig. 10. 



Since this first cable terminated at the Azores Islands where there 

 was no immediate demand for the full speed of which the cable was 

 capable, the first commercial operation was conducted at a speed of 

 only about 800 letters per minute. This was obtained with a standard 

 cable-code transmitter and a standard type of recorder used with the 

 signal-shaping amplifier. The cable was operated alternately in the 

 two directions as required to accommodate traffic, the reversal of 



