PROJECTILES CONTAINING EXPLOSIVES A. R. 135 



locity of propagation is at first much greater than that of sound, but 

 which rapidly diminishes until it becomes the same as sound. There 

 is thus produced an interruption of continuity and we Icnow that in 

 this case the difference in pressure existing at the front of the wave 

 and the medium in which the latter is propagated may attain to a 

 very notable value. 



Numerous researches have been made on this subject in France and 

 elsewhere. The more recent have been carried out by the commission 

 on explosives^ which has recognized that the limiting radius, ^^ of 

 dangerous eifects by the wave could be represented by the formula 



in which r represents a length expressed in meters, C the weight of 

 the charge in kilograms, and K a constant dependent on the nature 

 of the explosi/e and the degree of security sought. It follows from 

 this that for different charges the distances at which corresponding 

 mechanical effects are produced are prof)ortional to the square roots 

 of the weights of the charges. 



The detonation of 100 kilograms of melinite, for example, gave 

 rise to a shock wave at whose surface there existed a pressure greater 

 than 10 kilograms per square centimeter for a distance of 7 meters 

 about the center of explosion. At 10 meters the pressure was between 

 2 and 3 kilograms, and at 15 meters it had fallen to less than one-half 

 kilogram. Regarding the velocity of propagation of this wave we 

 find it to have been 800 meters per second in the vicinity of the center 

 of explosion, 635 meters at 5 meters farther away, 360 meters at a 

 distance of 50 meters, and then down to 250 meters per second, which 

 is the velocity of sound. 



It follows from the preceding that a person located at some meters 

 from the explosive charge will first be struck by the pressure from the 

 shock wave, which will be followed by a sharp and sudden depression 

 and movement of the air at high velocity toward the center of the 

 explosion, 



A fortuitous circumstance, recorded by M. Arnoux, has enabled us 

 quite recently to elucidate the order of magnitude of this depression 

 and to explain by the same the probable mechanism in numerous cases* 

 of dead bearing no apparent Avounds which have been observed on the 

 battlefield. 



Last January M. Arnoux received from a superior officer at the 

 fi'ont a pocket aneroid barometer which had been put out of service 

 by the explosion of a German shell at a distance of about three meters 

 from the instrument. On examination its parts were found intact 

 but it could not register because the two transmission levers con- 



^ Memorial des Poudres et SalpStres, 1905—6. fitude des effets a, distance des explo- 

 sions. M. Lheure, rapporteur. 



