268 LECTURE XXIX. 



agent in the astonishing effects produced by the explosion of gunpowder. 

 The initial elasticity of the fluid by which a cannon ball is impelled, ap- 

 pears, from Bernoulli's calculation, to be at least equal to ten thousand 

 times the pressure of the atmosphere, and upon the most moderate compu- 

 tation, from Count Rumford's experiments, to be more than three times as 

 great as this. The quantity of moisture, or of water of crystallization, con- 

 tained in the powder, is certainly too small to furnish steam enough for so 

 great an effect. We have no reason to suppose that the elasticity of a given 

 quantity of any aeriform fluid or vapour is increased more than about one 

 five hundredth for each degree of Fahrenheit that its temperature ib ele- 

 vated ; and if we suppose the heat to be raised to more than 5000 degrees, 

 the force of each grain of water converted into steam will only be increased 

 tenfold ; so that if the elasticity were 40 thousand times as great, the den- 

 sity must be 4 thousand times as great as that of ordinary steam, and the 

 whole space must be filled with an aqueous vapour almost twice as dense 

 as water itself. It is, therefore, probable that some other parts of the 

 materials assume, together with the water, the state of vapour, and possess 

 in this form a much greater elasticity than that of the steam : for the quan- 

 tity of fluids permanently elastic, which are extricated, must be allowed to 

 be wholly inadequate to the effect. 



The force of fired gunpowder is found to be very nearly proportional to 

 the quantity employed ; consequently, if we neglect the consideration of the 

 resistance of the atmosphere, the square of the velocity of the ball, the height 

 to which it will rise, and its greatest horizontal range, must be directly as 

 the quantity of powder, and inversely as the weight of the ball. Count 

 Rumford,* however, found that the same quantity of powder exerted some- 

 what more force on a large ball than on a smaller one. 



The essential properties of a gun are to confine the elastic fluid as com- 

 pletely as possible, and to direct the motion of the bullet in a rectilinear 

 path ; and hence arises the necessity of an accurate bore. The advantage 

 of a rifle barrel is principally derived from the more perfect contact of the 

 bullet with its cavity ; it is also supposed to produce a rotation round an 

 axis in the direction of its motion, which renders it less liable to deviations 

 from its path on account of irregularities in the resistance of the air. The 

 usual charge of powder is one fifth or one sixth of the weight of the ball, 

 and for battering, one third. When a 24 pounder is fired with two thirds 

 of its weight of powder, it may be thrown almost four miles, the resistance 

 of the air reducing the distance to about one fifth of that which it would 

 describe in a vacuum. 



Bullets of all kinds are usually cast in separate moulds: shot are 

 granulated by allowing the lead, melted with a little arsenic, to pass 

 through perforations in the bottom of a vessel, and to drop in a shower 

 into water. The patent shot fall in this process through a height of 120 

 feet : the roundest are separated by rolling them down an inclined plane 

 slightly grooved, those which are of an irregular form falling off at the sides. 



Condensed air may also be employed for propelling a bullet by means 



* New Experiments upon Gunpowder, by Benjamin Thompson, Ph. Tr. 1781, 

 p. 229. Consult Dalton, Manchester Memoirs, vol. v. 



