76 EXPLOSIONS BY INFLUENCE. 



On a loose or free soil the distances were less. When the 

 cartridge was suspended in the air, detonation did not take place 

 by influence, probably because the cartridge not being fixed 

 could easily recoil, thus diminishing the violence of the shock. 



However, there are trials on record which show that air is 

 sufficient to transmit detonation by influence, although less 

 easily, and when dealing with large masses. 



With dynamite containing less nitroglycerin (55% of nitro- 

 glycerin, and 45% of Boghead ashes) placed in cartridges of 

 a similar nature and laid on the ground, the trials made by 

 Captain Pamard gave shorter distances: D = 0'9 C. 



If metallic casings having less resistance be used, the distance 

 to which the explosion propagates itself is similarly reduced. 



Dynamite when merely spread about on the ground even 

 ceases to propagate the explosion. 



Experiments made in Austria have given similar results. 

 They have shown that the explosion communicates itself both 

 in the open air with intervals of 0*04 metre and through deal 

 planks 0*018 metre thick. In a leaden tube, with a diameter 

 equal to 0*15 metre and 1 metre long, a cartridge placed at one 

 extremity will cause the explosion of another cartridge placed 

 at the opposite end. 



The transmission of the explosion is more easily effected in 

 tubes of cast iron. Joints lessen the susceptibility of trans- 

 mission. 



3. The explosion thus propagated may grow weaker from one 

 cartridge to another and even change its character. Thus 

 according to experiments made by Captain Muntz at Versailles 

 in 1872, a first charge of dynamite when exploding direct had 

 made a crater in the ground the radius of which was 0*30 metre. 

 The second charge, which exploded by influence, produced a 

 hollow merely of 0*22 metre ; the effect of the detonation had 

 therefore become lessened. This diminution should become 

 manifest particularly towards the limit of the distances at which 

 the influence ceases. 



In the same way four tinplate screens were placed at intervals 

 of 0'040 metre, and a small cylinder of gun-cotton was placed 

 against each of them, the whole fixed on a board. At a distance 

 of 0*015 metre in front of the first screen, a similar cylinder 

 was exploded. All the cylinders exploded, but a progressive 

 diminution was observed in the cavities produced in the board 

 placed below each cylinder. 



According to these facts, propagation by influence depends 

 both on the pressure acquired by the gases and on the nature of 

 the support. It is not even necessary that this support should 

 be firm. 



It has been ascertained that these effects are not generally 

 due to simple projections of fragments of casing or of the neigh- 



