capable of operating under hydrostatic 
pressure, 
The use of fillers, such as small glass 
spheres, may permit construction of complete 
electronic circuits which will float. Figure 21] 
shows a 25-gram test block, containing a 
"payload" of resistors weighing 5-grams, float- 
ing in fresh water, Illustrated in Figure 22 is 
an encapsulated circuit of the velocimeter, 
similar to that used in Figure 19, The entire 
unit can be constructed so that its specific 
gravity is at least 1,1, The actual weight of 
the electronic circuit components in this instru- 
ment is only four ounces. By using the stand- 
ard technique of enclosing the electronic cir-~ 
cuits in a pressure-proof metal housing, the 
total instrument weight is increased by about 
25 pounds, The saving in weight and size 
which may be achieved by the development of 
instruments which can operate without 
pressure cases is obvious, 
To date, the results indicate that it is 
feasible to operate virtually every type of 
component required in electronic circuits under 
hydrostatic pressures up to 10,000 psig, at 
least for short periods of time, It appears 
further that circuits can be constructed of 
lightweight materials and encapsulated in 
filled resins to obtain operating units which 
are lighter than water. Such techniques may 
well become mandatory in construction of 
complicated oceanographic or acoustic instru- 
mentation systems, 
123 
