480 



276 



ARONS, SLIFKO, AND CARTER 



distances vertically above, vertically below, and 

 horizontally on each side of the charge. 



The center of the charge was in the plane of 

 the ring, and two charge orientations were used : 

 (a) axis of cylinder perpendicular to the plane of 

 the ring, (b) axis of cylinder horizontally oriented 

 in the plane of the plane of the ring. 



Dimensions were so chosen that the wire 

 structure supporting the gauges did not come in 

 contact with the bubble and was never damaged 

 or appreciably loosened by the forces of the 

 explosion. This insured against uncertainty in 

 gauge position owing to displacement of gauges 

 by the shock wave. 



5.4. The over-all depth of water was measured 

 by means of a fathometer, and all experiments 

 were performed in such depths that the charge 

 was always at least 150 ft. away from the 

 bottom. The depth of the charge was deter- 

 mined by the measured length of suspension 

 cable supporting the ring, the method being 

 very reliable since experiments were performed 

 in a region of negligible tidal currents, and the 

 suspension always hung vertically downward. 

 This is confirmed by the reproducibility of the 

 period measurements given in Table I. 



5.5. Continuous 600 ft. -lengths of Simplex 

 (F.O. 5879) signal free coaxial cable were used 



between the gauges and oscilloscopes, thus avoid- 

 ing occurrence of spurious cable signal for an 

 interval sufficiently long to allow faithful record- 

 ing of the first two bubble pulses. Cable effects 

 were further minimized by the relatively high 

 sensitivity of the gauges. The polythene core of 

 the cable rendered negligible any low frequency 

 distortion due to dielectric dispersion. The cables 

 were compensated in accordance with principles 

 discussed elsewhere.'' 



5.6. Recording equipment consisted of eight 

 oscilloscope channels* on the schooner "Re- 

 liance." In order to avoid low frequency distor- 

 tion, it was necessary to increase the input 

 impedance of the oscilloscopes by using cathode 

 follower preamplifiers. The final over-all time 

 constant of the recording circuits was about 500 

 millisec. 



A 110-v d.c. motor with variable armature 

 voltage was used to drive the rotating drum 

 cameras. Writing speeds were varied from 125 

 to 400 millisec. per revolution of the 10-inch 

 circumference drums. 



* R. H. Cole, "The use of electrical cables with piezo- 

 electric gauges," OSRD Report No. 4561 ; NDRC Report 

 No. A-306. 



* R. H. Cole, D. Stacey, and R. M. Brown, "Electrical 

 instruments for the study of underwater explosions and 

 other transient phenomena," OSRD Report No. 6238; 

 NDRC Report No. A-360. 



