1340 
description. In each case the limiting curve Fr for the 
analogous ideal gas is given for comparison. The two apparent 
families of solutions which are usually distinct for an ideal 
gas are undoubtedly physical regions of one double-valued 
family in the case of water-like substances. Typical three- 
shock configurations for given values of § and of @ are shown 
in the diagrams of fig. 18a, a'. The influence of ¥ is illustrated 
in the comparative cases of fig. 18b, b'. 
V. EXPERIMENTAL EVIDENCE 
The interaction of shock-waves in water was first studied 
by P. Libessart 12) at Oxford, England. In fig. 19, Plate I, 
a spherical shock-wave produced by, No. 8 detonator is shown 
reflected obliquely from a wall. From the four exposures we 
observe how "regular reflection" develops into "Mach reflection" 
(incipient at Srd exposure). In fig. 20, Plate I, shock-waves 
from two No. 8 detonators, fired simultaneously from opposite 
ends of an ebonite cylinder, have interacted to produce a Mach 
effect. It is likely that the central band is the region in- 
cluded between two surfaces of density-discontinuity (the optics 
of such photographs require further study). 
(See page 74 for insert.) 
D. P. Mac Dougall, G. H. Messerly, and E. M. Boggst4) of the 
Explosives Research Laboratory, Bruceton, Pa., have investigated 
the oblique collision of two intense shock-waves produced by 
the detonation of an inclined pair of pentolite sticks (1" 
diameter) in water. Figure 23, Plate III, illustrates a 
=I 5o0— 
