88 BELL SYSTEM TECHNICAL JOURNAL 



it into the developing tank. The second carries the paper through 

 the developing and fixing tanks. Each is adjustable in speed and con- 

 trolled separately. The speed of the main drive motor is adjusted to 

 best exhibit the phenomena that are being observed. Maximum speed 

 is about 130 inches per second, which gives a little over a hundredth 

 of an inch between crests of a 12,000 cycle wave. The motor con- 

 trolling the developing equipment is adjustable to give paper speeds 

 from two to ten inches a second. The faster the speed at which the 

 paper is exposed the more slowly will it be developed. 



Since the paper being exposed is moving faster than that being de- 

 veloped, a storage reservoir for undeveloped paper is provided as in- 

 dicated in the illustration. At the beginning of an oscillogram the 

 paper is pushed by the main drive roll in between the drive rolls of the 

 developing tank. Since these carry the paper at a lower speed than 

 the main drive, a loop of paper is formed between the two drive rolls 

 which passes into the storage tank. The amount of paper that can 

 be stored depends on the speed of exposure, and varies inversely with 

 it. At low speed the paper settles compactly in the tank and an entire 

 250 foot roll may be stored. At high speeds the paper does not have 

 time to settle properly, and only about fifty-five feet, corresponding 

 to about five seconds exposure, can be held. 



Fig. 14 — Rapid record oscillograph. Front pole face of galvanometer. Terminals 

 for the three-string elements are brought to knife contacts, which allows the string 

 mounting and pole piece to be readily removed from the galvanometer. 



Both motors having been started, operation of the oscillograph is 

 commenced by pulling out a lever which withdraws a knife blade from 

 the paper, and moves an idler pulley, which presses the paper against 

 the main drive roll. The paper is then run through the storage tank, 

 and the developing and fixing tanks as already described. After the 



