723 
pay Tare: 
Solving these two equations for CoVo we have 
Vy, 
CV = CVs Gs 
The unknown charge CoVg may therefore be determined from a known quantity 
of charge CyVs and the ratio of the voltage outputs. This voltage ratio 
is the ratio of the displacements on the cathode~ray oscillograph screen 
as recorded by the camera. In actual practice the standard condenser Ct 
was a part of the cable terminating circuit (corresponding to C2 in Eig. 10). 
In addition to the greater ease in calibrating, the Q-step allows an esti- 
mate of the cable response characteristics. For example, if the cable had 
low impedance due to dielectric or salt-water leakage, the Q-step fell off 
exponentially. The conditions under which the records were actually made 
were thus known, and pressure~time curves could be corrected when necessary 
from the Q-step record by the superposition theorems, 
(vi) Time standard, The standard frequency source commonly used on 
the RELIANCE for calibrating the time base was a multivibrator which was 
driven by a 100 kc/sec crystal-controlled oscillator [17]. Frequencies of 
25, 10, 5 and 1 kc/sec were available, Some of the earlier circuits for 
this multivibrator would allow it to lock in on some sub-multiple of the 
oscillator frequency other than the one desired but later designs overcame 
this difficulty. The multivibrators were checked in the field by a battery— 
operated, resistance-stabilized L-C oscillator which was stable to 0,1 per— 
cent, thus allowing any major discrepancy in frequency (due to the wrong 
interlocking) to be detected. These frequency standards were checked against 
the standard frequency of radio station WWV, 
(vii) Still-film cameras, The still-—film cameras omployed were mounted 
in a specially built camera hood fitted on the Dumont 208 oscillograph aval 
An £/2.0, 50-mm focal length lens was used with a manual flap swinging in 
front of the lens as a shutter. Diaphragm-type shutters were not found 
satisfactory because of trouble with the cable releases, The flap type 
shutter was very satisfactory since it was positive in action and shutters 
on several cameras could be very easily ganged to operate as once unite 
Cut film 2-1/) x 3-1/) in. was used in a Recomar holder fitting into a 
camera back which could be rotated to give four different exposures on a 
Ss ingle film. 
(viii) Sweeps When a still-film camera was used the cathodesray spot 
had to move across the screen at a uniform speed. This was done by means 
of a linear time base which swept across the screen once after being 
triggered, at’ the same time brightening the beam so that it recorded on the 
photographic film. Sweep speeds were avatlable from 125a1sec/in. to 12,5 
msec/in. For purposes of adjustment, both automatic intermittent single 
sweeps and continuous sweeps, in addition to triggered single swecps, could 
be obtained from this linear time base [17]. 
