604 



From (1), (2), (3) 



From (3), (4), (5) and (6) 



From (l) and (4) we get 



(2) ana (5) we get 



(3) and (6) we get 



Hence absolute value of v^ = 8.914 x 305 



= 2720 cms. oer second. 



Thus taking /O = 1; C = 15 x 10 cms. per second. 



we get o max = i P- Cv = 204 atmos. = 3000 lbs. /square inch 

 = 1.34 tons oor square inch. 



as the maximum pressure oroJucid By 500 lbs. T.N.T. at distance of 50 feet. 



From the deduced values for v , k ana t the values of S are calculated and entered above. 

 The comparative results are shown in the adjoining aiagram Figure 2. 



If Stokes viscous law is applicable the iDove value of k would lead to the conclusion that 

 the particles ire about 0,4 mm. in diameter. 



A number :f experiments have been made with mines, aeoth charges, ana war heaos. The 

 explosive, th= weight use*:, the ae-pth, the primer, nave all been varies. The methoc of experimenting 

 has been gradually imcrcveJ where experience shpweo the necessity, Discre:ancies occur from time 

 to tirrf, so that until the reason f;r these has been fully investigatel, it is net consiasred 

 desirable t; give final results. 4t the s^me time it is possible t; say with reasonable certainty 

 that the results s; far pbtaineo c;nfirm the view that f-^r the sane weight :f explosive the maximum 

 pressure is inversely proportional to the distance, while for the same distance the maximum pressure 

 appears to be nearly proportional to the squar' root ;f the weight of the explosive. The difference 

 between 3iff;rent jxplosives such us pure T.N.T. and different grades cf Anetcl d; not appear very 

 definite as far as rmximum pressure is c.:ncerneJ, but a final aecisicn must wait f?r further 

 experiments. As regarps megnituoe it appears that a 300 lb. oecth charge ",f 50/50 Amatol ortmsi 

 with 3 aiscs jf C,L. gives a maximum ;ressure of 1.15 tons per square inch at a aistance of 50 feet. 



The maximum pressures obtained by this method are in themselves very useful. Out the methpa 

 gives no information as to the time element in the explosive wave for which a very aifferent method 

 of procedur; is now being investigated. But the known speed of aetonatlon, say 5000 metres per 

 secono, in rouno numbers, ano the general aimensions of the mine, say i metre, suggest that the 



oraer cf magnitude cf the time from 

 will vary of course, with the exclc 

 figure and the known value of the nia' 



tiaticn to maximum pressure is of order id seconds. It 

 /e, the amjunt of it, ano tne manner of detonation, but this 

 mum pressure arc most useful as a guide in the a.-sign of 



the apparatus for me^isuring the time pressure sequence. 



The comparatively simply character of the primary wave from the explosion, as outlined, may 

 appear to be at variance with the observed fact that the damage to a vessel depends greatly on the 

 Position relative to the charge ano to the surface. 



Let us revert to Figure 1 ana consider the effects at a point " in the water, 



Thi- disturbance from the Image mine is ooccsite in sign to tne direct effect, Is less In 

 the properties r^ and r^ ana arrives later by the time taken t; traverse the distance (r - r ) at 

 the rate 1500 metres per secona (the speoc of the wave in water). N-w at any pjint the critrary 

 ana the reflected 3isturoances each rise t their maxirxjm in a very short tlrre, which we have seen 

 is -f order 1/10,C00 th :f a seccnj. If then r - r is 1 metre or say 3 feet, the Interval between 

 the two maxima would be 1/1, 500th of a second and tne two effects are practically separated. But 

 if fj - r^ is as small as 3 cm., the interval is only 1/50, 000th cf a second and thus small comcareo 

 with liio.oooth of a second as above. The two effects would thus tend to cancel each other, and 

 we thus see how to reconcile the apparent pandox that the resultant action may be small near the 

 surface, while at some depth there are two separate large shocks. 



I t may 



