204 



BELL SYSTEM TECHNICAL JOURNAL 



cantilever bar A iiUejjral with a massive L-shaped base, the entire 

 device having been milled from a single piece of steel. A given dis- 

 placement of the graduated screw B produces a greatly diminished 

 displacement of the movable electrode Ci. The dimensions of the bar 

 were so chosen that contact displacements of the order of 1 X 10"^ 

 cm. could be produced. The motion of Ci is made strictly linear by 

 means of the pivoted rod D and any slack motion is eliminated by the 



0.01 0.05 0.1 



APPLIED POTENTIAL IN VOLTS 



0.5 



t ig. 5 — The mean square contact noise voltage in a single carbon contact as a function 

 of the applied voltage. The contact resistance was held constant at 76 ohms. 



spring E. The contact is initially adjusted by the graduated screw F 

 on which the stationary electrode C2 is mounted. Ci consisted of a flat 

 polished disk of carbon like that used in the desk set transmitter, while 

 Ci w^as a composite carbon spheroid clamped securely between two 

 gold plated jaws. Both the carbon plate and the spheroid were coated 

 with a pyrolitic deposit of hard carbon. 



The noise in a large number of single carbon contacts, connected in 

 place of the transmitter in the input circuit shown in Fig. 2, was 



