525 
- 29- 
TABLE 
Oe 
Difference 
(v-v) 
ft./sec. 
Velocity V feet v 
per second 
Length of 
base feet 
Record No. Temperature 
“fe 
V,16 
17 
Corresponding 
waves ft./sec. 
Mean of 
all records 
The chief source of error in the velocities given in the above table is that involved in the actual 
measurement of the records. In the first series V2 to Vg, for example, the probable error due to this 
record, however, the error may be reduced. Taking into consideration all the above mentioned sources of 
error it seems probable that the velocity 4875 ft./sec. at 10.3°C is correct within limits of + 40 ft./sec. 
correct within the limits + 30 ft./sec. !t will be observed, however, that whilst the average of the 
first series gives a value of velocity of 10 ft./sec. lower than the known value for smat) ampTitude waves, 
Taking the mean of all observations the velocity of the large-amplitude pressure pulse is 4890 ft./sec. 
at 8.5°C as compared with 4865 ft./sec. for waves of very small amplitude. The difference between these 
for small amplitude 
10.3°C sy fatnat te Mean 4875 ft./sec, 4886 ft./sec. 
: oe 
cause in individual measurements is + 30 ft./sec. by taking a series of independent measurements of each 
Similarly it was considered that the value 4906 ft./sec. at 6.9°C obtained in the second series is also 
the average of the second series is 60 ft./sec, higher. It is difficult to account for this difference. 
values is small and uncertain. 
Growth of Gas Bubble. 
Reference has already been made above to the experimental observation that the rate of fall of 
pressure is proportional to the radius of the charge. This of course implies that the gas bubble formed 
at the instant of complete detonation expands approximately in accordance with ordinary gas laws. It is 
amatter of some theoretical and probably practical importance to measure the rate of expansion of the 
bubble, and consequently the rate of displacement of the water surrounding it, by more direct methods. 
This question has already been examined by Ramsauer” by the following method. A number of steel 
points at known distances from the charge are connected through insulated leads to corresponding 
electromagnets which are arranged to contro) markers on a Chronographic drum Normally, direct current 
passes through the points and returns through a large earth plate. When the charge is exploded, however, 
and the expanding gas bubble touches one of the points the current is cut off and the corresponding 
electro-magnet records the instant on the chronograph. Similarly for the other points. In this way 
the chronograph record indicates the arrival of the bubble at the successive points, where it is 
possible to deduce the velocity and acceleration of the boundary of the gas bubble. Using charges of 
dry gun cotton of 1 to 5 lbs. weight, it was found that the maximum displacement of the boundary was 
given dese. 
C. Ramsauer (Ann. der Physik 4 vol. 72 Heft 4. p.p. 265-284 August 1923) and Admiralty 
Technical Records Ac. 117. 
