741 
= 35 = 
attached to the two sides of the H, (Fige 3E). The distance between the 
two gauges was originally 2); ine then later 18, and finally 12 in. The 
12—in,. spacing was found to be satisfactory, easier to use, and more resis= 
tant to damage. 
(ii) Other methods of mounting. Piezoelectric gauges were sometimes 
attached directly to the spacer cable, This was usually not satisfactory 
because of reflections or signals picked up trom this cable. However, for 
certain types of measurement it was necessary to know the exact location of 
the gauges with the respect to the cable and to each other, and under these 
circumstances the H-frames could nat be used since they were free to rotate 
about the cable as it twisted and untwisted with the strain of the gear. 
In connection with mounting piezoelectric gauges there are certain 
points whicn should be mode. It was noted that when gauges were placed at 
four different locations with all piezoelectric gauge cables leading direct— 
ly back along the spacer cable, the large mass of these cables caused 
spurious signals to be produced in the gauges at the greatest distance from 
the charge. These spurious signals were eliminated yhen the four cables 
from the first two gauge positions were led up to the surface before reach— 
ing the third and fourth gauge positions. It was also found necessary to 
metallically ground by means of a long wire the copper tubes of the gauges 
at the four different gauge positions when the distances between positions 
were large. Before this metallic grounding was used, various disturbances 
were noted on the records of the far gauges at the time the shock wave 
struck the- near gauges. 
lhe Gauge and charge spacing 
One of the. most important details of any explosive measurement is to 
set up and maintain the desired oricntation between the charve and the 
various measuring instruments. [For RELIANCE work this has been done en= 
tirely with flexible cables. 
(a) Vertical components. — Various instruments and other gear were 
maintained vertically by means of drop lincs and masses sufficient to hold 
them reasonably straight. The drop lines (usually 5/l6-in. wire rope) were 
suspended from surface floats, The size of the surface floats depended upon 
the weight which had to he supportcd (Fig. 27). These surface floats were 
kept as small as possible consistent with the requircd buoyancy, so that the 
minimum drag on the floats was produccd as the gear was towed through the 
water. Surface floats have consistcd of 30= and 50-gal oil drums, of cmpty 
Mark ) or Mark 6 mine cases, or of mooring buoys of various sizes. The 
mooring buoy most commonly used was the 21-in, spherical buoy, Spherical 
floats of ll-gauge steel (manufactured by the Chicago Float Works) have also 
proved extremely durable. However, the largest size in which these could 
be obtained had a lin. diameter and was not sufficient for supporting 
heavy gear. For supporting the charge, oak barrels wore ordinarily uscd, 
These were less expensive than stcel drums ond their breakage did not matter 
since in this position dircctly pver the charge even stcel drums could usual- 
ly be used but once, The Mark ) or Mark 6 spherical mine cascs were very 
resistant to shock wave damage, but it was extremely difficult to attach 
