Method of Measuring Explosion Pressures. 487 



The velocity was also obtained approximately from the 

 interval between the arrival of the direct and reflected waves 

 at the vessel in the above experiments. The position of the 

 vessels and charge were known in each case, as well as the 

 depth of the water, and thus from the geometry of 

 the arrangement the path difference between the direct and 

 reflected wave could be determined. The time interval is 

 obtained from the plates on which the direct wave and echo 

 from the bottom are recorded. Supposing the bottom to be 

 a regular reflector, the velocity is obtained by dividing the 

 path difference by the corresponding time interval. In 

 Table IV. are given the results of a number of measurements 

 made in this way. 



Table IV. 



uT , AT Path difference rr - . ■, Velocity in feet 



rlate Jno. ■ ,. , lime m seconds. ".-irk i 



m teet. per sec. X 10 -3 . 



132 59 00110 5-4 



133 66-7 0-0109 6-1 



137 ...... 47'5 00091 5-2 



138 64 , 0-0128 5-0 



141 61-o 0-0117 5-3 



142 60-5 0-0111 5-4 



142 37 00065 57 



143 5G-5 0-0113 5"0 



149 59 . 00106 5-5 



149 43 000795 5-4 



150 68-5 0-0129 5-3 



150 43 00081 5-4 



152 68-5 0-0127 5-4 



154 ...... 69 0-0134 5"2 



155 57 0-0105 5-8 



156 36 0-0066 5-5 



157 49 0-00907 56 



Average veloeifcv=5-4xl0 3 feet/second. 

 * 

 It is evident from the table that the average value obtained 

 in this way for the velocity of the explosive wave is greater 

 than that determined from the direct measurements. The 

 second method is naturally not as accurate as the first, for 

 no account is taken of any irregularities in the bottom such 

 as stones, vegetable growth, etc. The results, however, are 

 an indication that the value 5100 feet per second is not too 

 high a value for the velocity of the wave. This is a greater 

 velocity than that attributed to sound, but the measurements 

 in this case were all made near the explosion. 



