1900.] on Some Modern Explosives. 345 



So much for the numbers ; now let me tell you of the velocities 

 with which, at the moment of explosion, the molecules were moving. 

 Taking first the high-velocity gas, the hydrogen, the molecules of 

 the gas would strike the projectile with a mean velocity of about 

 12,500 foot-seconds. You will observe I say mean velocity, and you 

 must note that the molecules move with very variable velocities. 

 Clerk Maxwell was the first to calculate the probable distribution of 

 the velocities. A little more than one-half will have the mean 

 velocity or less, and about 98 per cent, will have 25,000 foot-seconds 

 or less. A very few, about one in 100 millions, might reach the 

 velocity of 50,000 foot-seconds. 



The mean energy of the molecules of different gases at the same 

 temperature being equal, it is easy from the data I have given to 

 calculate the mean velocity of the molecules of the slowest moving 

 gas, carbonic anhydride, which would be about 2600 foot-seconds. 



I have detained you, I fear, rather long over these figures, but I 

 have done so because I think they throw some light upon the extra- 

 ordinary violence that some explosives exhibit when detonated. Take 

 for instance the lyddite shell, exploded by detonation, I showed you 

 earlier in the evening. I calculate that that charge was converted 

 into gas in less than the one 60,000th part of a second, and it is not 

 difficult to conceive the effect that these gases of very high density 

 suddenly generated, the molecules of which are moving with the 

 velocities I have indicated, would have upon the fragments of the 

 shell. 



The difference between the explosion of gunpowder fired in a close 

 vessel, and that of gun-cotton or lyddite when detonated, is very 

 striking. The former explosion is noiseless, or nearly so. The 

 latter, even when placed in a bag, gives rise to an exceedingly sharp 

 metallic ring, as if the vessel were struck a sharp blow with a steel 

 hammer. 



But I must conclude. I began my lecture by recalling some of 

 the investigations I described in this place a great many years ago. 

 I fear I must conclude in much the same way as I then did, by 

 thanking you for the attention with which you have listened to a 

 somewhat dry subject, and by regretting that the heavy calls made 

 on my time during the last few months have prevented my making 

 the lecture more worthy of my subject and of my audience. 



[A. N.] 



Vol. XVI. (No. 94.) 2 a 



