192 
IV. EFFECTS OF PRESSURE ca 32 
11. DAMAGING RANGE 
Hence 
in which D, is a constant. Thus on similar structures 
p=o,(i 
For a structure like an H4 mine case, of diameter L feet, and a charge of W pounds of 
TNT or amatol, ee 
D=7.6W’L * feet 
Or, we can say that the damage on any structure distant R from the charge is 
F(z) 
R°L 
where F' is a function depending on the type of structure. 
Seeking a physical basis for Hilliar's result, we note that neither the 
pressure nor the impulse varies as wr It could be stated, however, that an H4 mine 
case "begins to be damaged when the energy flux exceeds about 5 foot-pounds per square 
inch." Hillier is of the opinion, nevertheless, that this relation with the energy 
is fortuitous and that the significant quantity is more likely to be the time inte- 
gral of the excess of pressure over a fixed value, |(p-k)dt, where k depends upon 
the structure. On this view, an H4 mine case begins to be damaged when JQ- 200) dt 
exceeds about 360, p being in pounds per square inch and ¢t in milliseconds. 
V. SURFACE PHENOMENA | 
V. SURFACE PHENOMENA OVER AN EXPLOSION 
The surface of the water over an explosion behaves in a manner that is full 
of interest and often spectacular. These phenomena are of comparatively little prac- 
tical importance, however, and will only be summarized here very briefly. 
Three distinct effects are noted: 
(a) At the instant of the explosion, the surface of the water seems to be 
agitated, and a light spray may be thrown up. This effect is not noticeable if the 
explosion is very deep. 
(b) During the next second or two after the explosion, the water rises into 
a flattish "dome" which is often whitish in color and may attain a height of 50 feet 
or more. As the depth of the explosion is increased, the maximum height of the dome 
diminishes, and finally no dome is formed (e.g., there is none from 40 pounds of TNT 
or amatol 60 feet deep or 300 pounds 150 feet deep). 
(c) Plumes of spray may be thrown up. If the charge is only a few feet below 
the surface, the plumes break through the dome while the latter is still rising, and 
