i8o Instantaneous Pressures ?r. ihe Explosion-Wave. 



opposite directions be to largely increase the pressure at the 

 point of contact ? By analogy one might suppose that such 

 would be the case ; but, on the other hand, since the 

 explosion travels much faster than any wave in the unburnt 

 gas the explosion-wave is always, as it were, dashing on a 

 dead wall and piling up pressure, and no further effect, it 

 might be argued, could be produced when it meets and is 

 repulsed by a similar wave. It seemed, however, possible 

 if the wave is propagated partly by the movement of heated 

 yet unburnt molecules in the wave front — that these mole- 

 cules on coming into collision would cause a measurable 

 increase of temperature and pressure in the wave. We 

 have not been able to measure any such increase by this 

 rough method of trial. The explosion tube, some 

 3 feet from the firing point, bifurcated into two 

 arms like the letter Y. The two arms were bent round 

 nearly to meet, and the junction was effected by a piece of 

 glass tube inserted in the gap. The centre of the glass 

 tube was exactly equi-distant from the fork by either arm ; 

 consequently the explosion-wave, dividing into two at the 

 fork, traversed the two arms and came into collision in the 

 middle of the glass tube. By a suitable tap, one arm could 

 be closed, and the explosion then traversed the glass tube 

 only in one direction. Experiments made with hydrogen 

 and oxygen, with equal volumes of cyanogen and oxygen, 

 and with the same mixture diluted with nitrogen as before, 

 showed no appreciable difference between the pressures 

 produced in the glass tube when the flame went in 

 one direction only and when the two explosion-waves met 

 end on. Pieces of the tube, which broke in the hydraulic 

 press at 63 atmospheres, broke both ways equally in the 

 explosion apparatus : pieces of the tube, which broke 

 in the hydraulic press at 84 atmospheres, stood the 

 explosion both ways equally. If the collision had caused 

 the pressure to rise by % we ought to have detected it. 



