578 
Figure 5a 
This is a view of the gage element before the rubber coating is molded around the crystal. 
Figure 5b 
~ This is a view of the completed gage. 
Figure 5 - TMB Tourmaline Gage for Determining 
Underwater Explosion Pressures 
in the type of insulation and cable employed. The construction of this gage 
and of a TMB copper cable have been described in detail elsewhere (18); they 
are shown here in the photographs, Figures 5a and 5b. Tourmaline is sensi- 
tive to isotropic pressure and therefore requires no mount. Thus the fre- 
quency of the lowest mode of vibration of the tourmaline gage is much greater 
than that of the quartz gage. The crystals employed have approximately the 
same area and sensitivity as the quartz crystals. The tourmaline crystals 
are insulated by molding a sheath of rubber with a low sulphur content about 
the crystal and that part of the cable to which it is attached. 
A modified form of this gage has been used to obtain load-time rec- 
ords at a surface of an underwater structure exposed to explosive loading. 
The rubber insulation is not only molded about the crystal and the copper 
cable but also to a brass plate; see Figure 6. This plate is then bolted to 
the structure. The structure must be heavy enough to be unaffected in its 
deformation or its motion by the screws or by the weight of the brass plate. 
Pressure records obtained in this manner are compared with "open-water" 
records later in this report. 
