1314 
other types of interaction can be discussed (cf. Appendix B 
for proofs of two interesting results); they are summarized 
in Table 3, which includes also the ideal gas results for 
comparison. It is significant that a water=like substance 
does not always behave like an ideal gas (fictitious for ¥Y >5/3) 
having the same value of ¥ . For example, in the case of 
water the overtaking of one shock-wave by another results always in 
a rarefaction being reflected, whereas there may be a reflected 
shock for the analogous ideal gas. Then, too, for a rarefaction 
overtaking a shock-wave the reflected wave is always a shock in 
water, but it may be a rarefaction in the ideal gas. Moreover, 
the kinds of phenomena that occur in water=-like substances are 
independent of the value of an not sO in the gamut of so-callec 
ideal gases where (ics 5/3 is a peculiar mathematical boundary. 
Typical instances of interactions in water-lixe substances are 
illustrated in fig. 6a, b, c, and de 
alae OBLIQUE REFLECTION OF SHOCKS 
The oblique collision of two similar shock-waves 
is mathematically equivalent to the oblique reflection of a 
single shock. Hence consider a plane shock-wave i (efi, £15). 
7a) moving with constant velocity in a water-like suostance 
’ and incident at an angle @on an infinitely wide, plane 
rigid wall. The reflection is said to be "regular" 1) af 
= BB oc 
