is equal to half the time difference between the bottom and 
the surface=bottom reflections for depths of water greater 
than 1000 fathoms (see Figure 2). It is then an easy matter 
to calculate, knowing the velocity of sound in the water 
from the bathythermograph observations, the time it took the 
snot instant to travel from the shot point to the shooting 
ship, 1. e., the shot instant correction. 
III. Sinking Rates of Explosive Charges 
Unless the shot record is recorded photographically, 
it is not possible to read the bottom-surface bottom reflection 
interval with consistency; and even on some of the photographic 
records it is not possible to read this interval due either to 
blocking of the amplifier or excessive noise level. For these 
shots it is necessary to use the data from those shots on 
which this interval could be reade This is most easily done 
by referring to the sinking rate graphs (see Figures 3 - 12). 
These are plots of twice the depth of the explosion, i. 6., 
the bottom-surface bottom interval, versus the time over the 
side.e Knowing the time over the side the depth of tie explosion 
can then be read off the graphs. ‘The scatter of the plotted 
points about the line that is drawn is + .01 second for the 
depth of the explosion. It can safely be assumed that any 
readings taken from these graphs will be accurate to that 
figure, ire Ye fanqge  of% whe plbserved = porns, 
All the charges that were used in plotting these 
points were fired by safety fuse. The charges consisting of 
