TWO ORDERS OF WAVES. 79 



But this ceases to be true when passing from one medium to 

 another. 



5. If the chemically inactive substance which transmits the 

 explosive movement be fixed in a given position on the ground 

 or on a rail on which the first cartridge has been placed, or 

 again, held by the pressure of a mass of deep water, in which 

 the first detonation has been produced, the propagation of the 

 movement in this matter could scarcely have taken place except 

 under the form of a wave of a purely physical order, a wave, the 

 character of which is essentially different to the first wave 

 which was present at the explosion, the latter being both of a 

 chemical and physical order, and having been developed in the 

 explosive body itself. While the first or chemical wave pro- 

 pagates itself with a constant intensity, the second, or physical 

 wave, transmits the vibration starting from the explosive centre, 

 and all around it, with an intensity which diminishes in inverse 

 ratio to the square of the distance. In the immediate neigh- 

 bourhood of the centre, the displacement of molecules may 

 break the cohesion of the mass, and disperse it, or crush it by 

 enlarging the chamber of explosion, if the experiment be carried 

 out in a cavity. But at a very short distance, and the greatness 

 of this depends on the elasticity of the surrounding medium, 

 these movements, confused at first, regulate themselves, so as to 

 give rise to the wave properly so called, characterised by sudden 

 compressions and deformations of the substance. The amplitude 

 of these undulatory oscillations depends on the greatness of the 

 initial impulse. 



They progress with an excessive rapidity, at the same time 

 constantly decreasing in intensity, and they maintain their 

 regularity up to points at which the medium is interrupted. 

 There these sudden compressions and deformations change their 

 nature, and transform themselves into an impelling movement, 

 that is to say, they reproduce the shock. If then they act on a 

 fresh cartridge they will cause it to explode. This shock will 

 further be attenuated by distance, owing to the decrease thus 

 introduced into its intensity. Consequently the character of 

 the explosion may be modified. The effects will thus diminish 

 up to a certain distance from the point of origin, beyond which 

 distance the explosion will cease to produce itself. 



When the explosion has taken place in a second cartridge the 

 same series of effects is reproduced from the second to the third 

 cartridge, but they depend upon the character of the explosion 

 in the second cartridge and so on. 



6. Such is the theory which appears to the author to account 

 for explosions by influence, and for the phenomena which 

 accompanies them. It rests on the production of two orders of 

 waves, the one being the explosive wave, properly so called, 

 developed in the substance which explodes, and consisting of a 



