114 



NATURE 



[May 31, 1900 



the explosion vessel is very striking. In four seconds after the 

 explosion the pressure is reduced to abjut one-half, and in 

 twelve seconds to about one-quarter. 



explosion ; and knowing all these points with very considerable 

 accuracy, we should be able, from the study of the curves to 

 which I have drawn your attention, and which can be obtained 



I now show you (Fig. 10) similar curves for cordite 0*35 inch from different densities of gas, to throw considerable light upon 



the kinetic theory of real, not ideal gases» 



TIME IN SECONDS . 



Fig. 



in diameter, or about fifty times the section. Here you see 

 that the time taken to consume the charge is longer. The effect 

 of inertia is still very marked, although much reduced. The 

 true maximum pressure is little over 8 5 

 tons, but after the first third of a second 

 the two curves run so close together that 

 they are indistinguishable. 



Again, you see the pressure is reduced 

 by one-half in four seconds, and in a little 

 more than twelve seconds again halved. 



The last pair of curves I shall show 

 (Fig. 11) you was obtained with cordite 

 0"6 inch in diameter, or nearly 150 times 

 the section of the rifle cordite. With this 

 cordite the combustion has been so slow 

 that the effect of inertia almost disappears ; 

 it is reduced to about half a ton per square 

 inch. The maximum being nearly the 

 same as in the last set of experiments. 

 The time of combustion indicated I have 

 called slow, but it is about "06 of a second, 

 and the whole of the experiments show a ■ . <. • 



most remarkable regularity in their rate of 

 cooling, the pressures at the same distance 

 of time from the explosion being in all 



cases approximately the same — as, indeed, they ought to be. The 

 density being the same and the explosive the same, the only differ- 

 ence being the time in which the decomposition is completed. 



at temperatures and pressures far removed 

 from those which have been the subject of 

 such careful and accurate research by many 

 distinguished physicists. 



The question, as I have said, involves 

 some very considerable difficulties ; never- 

 theless, I am not without hope that the 

 experiments I have been describing may, 

 in some small degree, add to our know- 

 ledge of the kinetic theory of gas. 



That wonderful theory faintly shadowed 

 forth almost from the commencement of 

 philosophic thought, was first distinctly 

 put forward by Daniel Bernoulli early in 

 the last century. In the latter half of the 

 century now drawing to a close the labours 

 of Joule, Clausius, Clerk Maxwell, Lord 

 Kelvin and others have placed the theory 

 in a position analogous and equal to 

 that held by the undulatory theory of 

 light. 



The kinetic theory has, however, for us 

 artillerists a special charm, because it in- 

 dicates that the velocity communicated to a projectile in the 

 bore of a gun is due to the bombardment of that projectile 

 by myriads of small projectiles moving at enormous speeds, and 



It appears to m.e that, knowing from the experiments I have 

 described, the volume of gas liberated, its composition, its 

 density, its pressure, the quantity of heat disengaged by the 



NO. 1596, VOL. 62] 



Fig. 



parting with the energy they possess by impact to the pro- 

 jectile. 



There are few minds which are not more or less affected 

 by the infinitely great and the infinitely 

 little. 



It was said that the telescope wnich 

 revealed to us infinite space was balanced 

 by the microscope which showed us the 

 infinitely small ; but the labours of the 

 men to whom I have referred have intro- 

 duced us to magnitudes and weights in- 

 finitesimally smaller than anything that the 

 microscope can show us, and to numbers 

 which are infinite to our finite compre- 

 hension. 



Let me draw your attention again to 

 this figure (Fig. 2) showing the velocity 

 impressed upon the projectile, and let me 

 endeavour to describe the nature of the 

 forces which acted upon it to give it its 

 motion. I hold in my hand a cubic centi- 

 metre, a cube so small that I daresay it is 

 hardly visible to those at a distance. Well, 

 if this cube were filled with the gases pro- 

 duced by the explosion at 0° C. and atmospheric pressure, there 

 would be something over seven trillions, that is, seven followed 

 by eighteen cyphers, of molecules. Large as these numbers are. 



