2. 
961 
Table XI esults the evaluation o; e_consti 
Film No. Point No. R|-r r'- Dp ) 
EK hier (4in.) ( 800) 
536 22 0.61 3.15 14.76 39,1 
537 5a 0.63 3.39 14.72 Aus 
537 12 0.94 3.23 Verh 39.6 
536 § 0.97 3.68 14.03 43.8 
537 18 1.13 3.09 13.71 38.1 
Av. 0440.4 sees average deviation from mean = #1.7 & sec, 
It will be noted that there is no systematic trend of Q, with distance of 
the point selected for calculation behind the shock front ( |R\ = ray). 
Grid in same plane with charge; charge directly in front of camera; spherical shock waye 
If the experimental set-up is such that the plane of the grid is perpendicular to 
the optical axis of the camera with the center of the charge at this point of inter- 
section, then the peak pressure of the shock wave may be calculated as follows: Refer- 
ring to Fig. 136, G is the position of the camera; S is the shock wave; O is the charge; 
OG is the grid (perpendicular to the plane of the paper); R is the point at which the 
given light ray passes through the shock front; r and r' are the true and apparent 
points of intersection of a pair of grid lines, respectively. A construction line is 
drawn from 0 perpendicular to Rr'. As in Sec. 1, (a), the assumption is made that the 
pressure from R to r is constant. y is the ratio of the index cf refraction over this 
range to the index of refraction outside the shock wave. 
The quantities fp» gé, 9, Rr', Rr, S, and § are successively determined by the 
following equations: 
ten = a (I1-34) 
OR cos (f -8) = Or! cos /3 (11-35) 
@ = 180° - (09+ 6-8) = e- 9+ (11-36) 
By the law of sines, 
2: = #in (90° -4) (11-37) 
By the law of cosines, 
Rr = (Rr)“ + (rr*)* - 2 (Rr)(rr') cos (90° “B) (II-38) 
Again by the law of sines, 
sin =. sin (90° -@ ) (11-39) 
rr? Rr 
By Snell's lew, 
= —— § =e (II-40) 
The corresponding pressure is then obtained from Table X. After calculations have been 
made for several grid line intersections, the peak pressure is determined by the method 
described in Section 1 of Appendix II; namely, by plotting the calculated pressures 
against corresponding distances of the mid-point of Rr from the shock front, and 
extrapolating to zero distance from the shock front. 
15518 
