344 Sir Andrew Noble [March 23, 



Clausius, Clerk Maxwell, Lord Kelvin, and others have placed the 

 theory in a position analogous and equal to that held by the undula- 

 tory theory of light. 



The kinetic theory has, however, for us artillerists a special charm, 

 because it indicates 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 parting 

 with the energy they possess by impact to the projectile. 



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 which 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 introduced 

 us to magnitudes and weights infinitesimally smaller than anything 

 that the microscope can show us, and to numbers which are infinite 

 to our finite comprehension. 



Let me draw your attention to this diagram (Fig. II.) 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 centimetre, 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 produced 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, they occupy but a very small fraction of the con- 

 tents of the cubic centimetre, but yet their number is so great that 

 they would, if placed in line touching one another, go round many 

 times the circumference of the earth, a pretty fair illustration of 

 Euclid's definition of a line. 



These molecules however are not at rest, but are moving, even at 

 the low temperature I have named, with great velocity, the molecules 

 of the different gases moving with different velocities dependent upon 

 their molecular weight. Thus, the hydrogen molecules, which have 

 the highest velocity, move with about 5500 foot-seconds mean velo- 

 city, while the slowest, the carbonic anhydride molecules, have only 

 1150 foot-seconds mean velocity, or about the speed of sound. 



But in the particular gun under discussion, when the charge was 

 exploded there were no less than 20,500 cubic centimetres of gas, 

 and each centimetre at the density of explosion contained 580 times 

 the quantity of gas, that is, 580 times the number of molecules, that 

 I mentioned. Hence the total number of molecules in the exploded 

 charge is 8^ quadrillions, or let us say approximately for the total 

 number eight followed by twenty-four cyphers. 



It is difficult for the mind to appreciate what this immense num- 

 ber means, but it may convey a good idea if I tell you that if a 

 man were to count continuously at the rate of three a second, it 

 would take him 2G5 billions of years to perform the task of counting 

 them. 



