FIRE-BALLS. 223 



a speed of one-hundredth part of the required amount, 

 and even for this a charge of gunpowder, certainly not 

 less than a quarter of a pound, would be consumed. If a 

 cannon of amazing strength and of ideal efficiency could 

 be conceived, in which all the energy of the exploding 

 powder should be usefully concentrated upon communicat- 

 ing velocity to the projectile, we should find that to double 

 the speed the charge must be quadrupled. To treble the 

 speed we should have to increase the charge ninefold. If 

 the speed were to be increased ten times, we must put one 

 hundred times as much powder into the cannon. Finally, 

 if we could procure a piece of ordnance strong enough and 

 gunpowder rapid enough to impart meteoric velocity to the 

 missile, a charge would be necessary which is ten thousand 

 times as great as the quarter of a pound that is sufficient 

 under the conditions of ordinary artillery. This argument 

 shows 'us that the energy of an entire ton weight of gun- 

 powder would be required to impart to a stone one pound 

 in weight the velocity of an ordinary fire-ball. 



Whatever may have been the original source whence 

 the meteor acquired its energy (and this is a point on 

 which I do not at present make any remark), that energy 

 will be retained so long as the meteor retains its velocity. 

 Even if the meteor moved through empty space for a 

 million years, it would still be able to restore, if its motion 

 were arrested, the precise quantity of energy which it had 

 originally received. Hence, when the supreme moment 

 has arrived, the meteor expends in the throes of its disso- 

 lution all the energy it contains. Everything that the 

 energy liberated by the explosion of a ton of gunpowder 

 can dr that meteor weighing only a pound is competent 



