Theory of Explosions. 175 



there is any surprise, it would seem more fitting that it 

 should be exhibited at the detonation which large charges of 

 nitro-glycerine seem able to effect. 



This fact would tend to show merely that nitro-glycerine 

 has a velocity very near the critical point for gun-cotton, so 

 much so, that when large charges are employed the accele- 

 ration in the explosion of the nitro-glycerine is sufficient to 

 pass the limit. We know from Dixon's work on gases that 

 at first the explosion gains in velocity till the steady velocity 

 of detonation is obtained ; and there seems no reason against, 

 but, on the other hand, every probability in favour of, the 

 same thing taking place in nitro-glycerine. 



Above and beyond this the difference in the mode of appli- 

 cation of the two detonators must be taken into account. In 

 Abel's experiment the fulminate was enclosed in a tube of 

 copper or tin plate, while the nitro-glycerine was merely 

 applied in a capsule whose diameter was large compared with 

 its depth. The upper end of the fulminate tube was probably 

 closed by the electric firing apparatus; and this, as was shown 

 by the experiments in water, already described, together with 

 the fact that the fulminate was fired at the top, would give it 

 an enormous advantage. For there is considerable proba- 

 bility that in explosions of high velocity in air, the final 

 mode of " break-down " of the gas liberated is very depen- 

 dent on the initial conditions, just as I found it to be in 

 water. The nitro-glycerine was deprived by Abel of these 

 advantages ; and for these and the reasons above mentioned, 

 though it was able to blow blocks of compressed gun-cotton into 

 powder, and even to cause some of this powder to penetrate 

 the hard wood of the support, it failed to cause detonation. 



The other apparently anomalous facts observed by Abel 

 require further treatment, and most of all those explosions by 

 influence which seem, at first sight, only explicable by some 

 theory such as that of synchronous vibrations suggested by 

 Abel himself. 



On the Hypothesis of Synchronous Vibrations. 

 The difference in the behaviour of nitro-glycerine and 

 fulminate of mercury regarded as detonators, led Abel to 

 suggest that there might be some synchronism between the 

 vibrations caused in air or ether by the latter explosive, and 

 the natural period of vibration of a gun-cotton molecule. At 

 all events, the supposition is made that fulminate of mercury 

 when exploded can produce vibrations which are not pro- 

 duced by explosions of nitro-glycerine ; and that the superior 

 detonating power of fulminate of mercury may be due to the 



