526 
AG 
3 
given by y max = 159.3 VF cms. 
where W is weight in grams and P is the total external pressure (atmospheric + head of water). In the 
case of a particular charge of 16.10 grams of dry G.C. fired at a depth of 500 cms. it was found that 
the radius of the bubble passed through the values 50, 100, 200, 300 and 400 cms. at times corresponding 
to 44, 60, 106 and 125 x One second respectively from the instant of detonation. From observations 
of this nature the speed of water displacement at varying distances and depths was determined. 
Using piezo electric records of the p/t sequence of explosions, Butterworth has dealt with the 
question of expansion of the gas bubble theoretically. Ramsauer's experimenta) results are in good 
agreement with the theoretical deductions. 
Experiments were commenced during the present investigation to test a modification of Ramsaver's 
method but no opportunity offered for completing the work. It may be of interest, however, to outline 
the method for future use with large charges - Ramsauer has only applied his method to charges up to 
about 5 Ibs. weight. In the proposed modification a number of points In the sea are supp?led with A.C. 
of known frequency, The potential drop across the points and earth return is Indicated on the cathode 
ray oscillograph. As the bubble passes each point in succession the voltage changes corresponding are 
indicated by a change of amplitude of the A.C. wave on the oscillograph. Traversing the spot in the 
usual manner therefore should give an A.C. record showing a ‘stepped’ appearance, each ‘step’ indicating 
the arrival of the bubble at one of the points. The instant of firing the charge Is Indicated by the 
spot commencing to move when the pressure switch is closed. The time-intervals between the steps are 
known from the knowledge of the A.C. frequency. The preliminary tests of the method indicated, however, 
that the phenomena are not so simpleas was at first supposed. Thus it was found that the bubble on 
arriving at the first ‘point’ instead of increasing the effective resistance of the point actually 
reduced It to a very small value, thereby masking the effect of the progress of the bubbte over the 
succeeding points. There can be no doubt that the interior of the bubble in these early stages of 
expansion is a good electrical conductor, this being due, no doubt, to the intense fonisation due to 
the high temperature of the newly formed gas*. With a little modification, however, to meet such 
practical difficulties, there appears to be no serious reason why the method should not be developed so 
as to be of service in measuring the rate of growth of bubble for large charges. 
