938 
-4- 
aistance. At a distance of 1 Inch the Intensity is 20.6 tons/sq.in. The figure derived from 
the velocity of the shock wave Is much lower, being only 14.2 tons/sq.in. The ‘reason for this 
discrepancy is not clear, but it seems that the value based on the shock wave velocity entalls 
fewer assumptions about the machanism involved and is the more trustworthy proviced the measurement 
of this velocity is sufficiently accurate. We have assumed that the drum camera records give 
the initial velocity of the surface but it is not certain that this Is the case, it seems 
probable that a layer or scveral lay2rs break away from the water and are orojected uowards. 
{f the first layer is very tnin Its velocity snoulg be v, as given in the table but the thickness 
depends on the tension at which cavitation occurs, while the tendency of the water to break up 
intc dropists may also affect the measured velocity. 
The effect of oblique incidence. 
A simple tneory based on yeometrical reflection of the oressure wave as an equal tension 
wave shows that for an angle of inciaence @ the surface velocity Is v4 COS @ where v_ is the 
velocity for normal Incidence. The velocity of the water surface for angles of Incidence 0° 
to 60° is obtained from Figure 2. Dividing these values by cos O we get V, as a function of 
distance from the detonator, Im Figure 6 these values are shown and it aocears that the values 
of va deduced from the oblique reflection are considerably higher than those derlved from normal 
Incidence, 
The reason for this discreoancy as also for the different intensities aerived from water 
velocity and shock wave velocity is not apparent. The ohenomencn of the rising water surface 
may be more comolex than was supposed, Careful observation of the drum camera record for a 
detonator at 1 inch depth shows that the water surface Immeaiately above the detonator Is 
strongly decelerated for the first inch or so and then malntains a more or less constant speed 
or may sven be accelerat2d, 
References. 
(1) Lano's Hydrodynamics, uth Zoition, Ch. 10, 2.497 
(2) "Pressure=time curves for sud-marine explosions (Second paper)" by 
WeG. Penney and H,K, Dasyuota. 
