350 LECTURE XXIX. 



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

 the pressure of the atmosphere, and upon the most moderate computation, 

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

 this. The quantity of moisture, or of water of crystallization, contained 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 fivehundreth 

 for each degree of Fahrenheit that its temperature is elevated ; and if wt 

 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 density 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 quantity 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 di- 

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

 Count Rumford, however, found that the same quantity of powder exerted 

 somewhat more force on z 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 di- 

 rection 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 



