170 Mr. R. Threlfall on the 



initial conditions could lead to great variations in the result. 

 The position of the firing-point was the least satisfactory part 

 of the experiments ; and it seems probable that when the 

 gauges did not go as they were expected to go, the change 

 of effect was to be traced to imperfect centering of the firing- 

 point; about 10 per cent, of experiments would decline to 

 travel on the paths laid out for them. 



Some considerable difficulty was experienced in making the 

 tank water-tight. The continual shock of explosion stended to 

 produce leaks, and for some time this was very tiresome. 

 Mr. Walker, however, recollected that the introduction of a 

 little horse-manure into the tank was a method sometimes 

 employed for stopping leaks, and on trying it we found it 

 succeeded in absolutely stopping each leak as it was caused 

 within a very few minutes ; the fine particles having about 

 the same density as water remain suspended for a long time 

 and get carried into the holes as soon as a leak appears. 



These experiments leave very little doubt in my own mind 

 that the direction in which the maximum explosive effect is trans- 

 mitted will, in a great measure, depend on the initial arrangement 

 of surrounding obstacles ; at all events, when the explosion is 

 caused by fulminate of mercury and small charges are used. 



The shock of an explosion must be transmitted in one or 

 more of three different ways : — 



I. By actual bodily motion of the products of explosion 

 through the surrounding medium, either alone or becoming 

 gradually more and more mixed up with the medium itself, 

 which is thereby also set in motion. 



II. By an undulatory motion set up in the medium. 



III. By a vortex-ring motion. 



In the explosion of gunpowder, and other slow explosives, 

 the energy is doubtless transmitted chiefly by I. and II. 



The distance to which a considerable quantity of the energy 

 may be conveyed by means of waves of comparatively great 

 amplitude is in some cases remarkably great. This is evi- 

 denced by the effects produced by the explosion of powder 

 magazines. In the case of the fulminates of mercury and 

 silver, gun-cotton and nitro-glycerine, that is explosives of the 

 class examined under water, the effect falls off very rapidly 

 with the distance, and in water, at all events, is of a directed 

 character. 



This would point to the third mode of transmission being 

 in these cases of some importance; and if we consider the 

 way in which the products of explosion escape, we shall find 

 that the conditions for the production of vortex motion do in 

 fact exist. Let there be a sphere of fulminate of mercury 



