DETONATION OF HIGH EXPLOSIVES OR BY THE IMPACT OF BITLLETS. 447 



whole curve as iu the manner illustrated in fig. 3. Such a change of form analogous 

 to the change preparatory to breaking which a wave experiences as it advances into 

 shallower water would not be detected by these experiments, and it is not impossible 

 that it occurs to some extent. 



(b) Reflection and Effect of the Joint. The simple harmonic pressure-wave which 

 is propagated without change of type is accompanied by a distribution of shearing- 

 stress across the section. This shearing-stress depends on the square of the ratio yo, 

 and is small. That it plays no important part in these experiments is shown by the 

 fact that if there be a joint in the long rod the results are unaltered. Such a joint 

 transmits the pressure, but stops the shearing-stress part of the wave. As might be 

 expected, it was found that the faces of the joint must be a carefully scraped fit if 

 the wave is to pass it unaltered. 



The small magnitude of the shearing-stress is the foundation of the assumption 

 that the wave is perfectly reflected at the free end. Strictly accurate reflection is 

 not possible. A reflected wave which is exactly the same as the incident wave, except 

 that the signs of all the stresses are reversed, will when combined with the incident 

 wave give no normal force over the free end. The shearing-stresses corresponding to 

 the two waves do not, however, neutralise each other, but are added, hence accurate 

 reflection can only be brought about by the application of a distribution of shear over 

 the free end. The shear required is, however, of the order -/a* and the experiment 

 with the joint shows that its effects may be neglected. 



(c) Effect of the Diameter of the Rod. The pressure exerted by the bullet is 

 confined to a comparatively small area in the centre of the end ; whereas the pressure- 

 wave travelling without change of type implies a nearly uniform distribution of 

 pressure over the section. The question of the nature of the wave developed under 

 such conditions seemed quite intractable mathematically, but from general 

 considerations it appeared probable that it would not differ greatly from that of 

 wave originated by a uniform pressure distribution. In order to te* this poi 



2000 feet per second. 



