SCIENCE OF COMMON THINGS. 35 



Properties of a gun. Range of cannon. Explosive substances. 



At least 14,750 pounds upon every square inch of 

 the surface which confines it. 



198 What are the essential properties of a gun ? 



To confine the elastic fluid generated by the explo- 

 sion of the powder as completely as possible, and to 

 direct the course of the ball in a straight or rectilinear 

 path. 



199 Why will a rifle send a ball more accurately than a musket, or 

 ordinary gun ? 



The space produced by the difference of diameter 

 between the tall and the bore of the gun greatly di- 

 minishes the effect of the powder, by allowing a part 

 of the elastic fluid to escape before the ball, and also 

 permits the ball to deviate from a straight line. The 

 advantage of the rifle-barrel is chiefly derived from 

 the more accurate contact of the ball with the sides of 

 its cavity. 



J3OO To what distance may a ball be thrown by a twenty-four pounder f 



"With a quantity of powder equal to two-thirds the 

 weight of the ball, it may be thrown about four miles. 



The effective range of a twenty-four pounder is, however much less 

 than this. 



SOI How much further would the same ball go, were the resistance of 

 the air removed ? 



About five times the distance, or twenty miles. 



2OS Why is gunpowder always manufactured in little grains f 



In order to cause it to explode more quickly, by faci' 

 litating the passage of the flame among the particles.* 



2O3 By what terms are cannon of different sizes distinguished '? 



By the weight of the hall which they are capable of 

 discharging. Thus, we have 68-pounders, 24-pounders, 

 18-pounders, and the lighter field-pieces, from 4 to 

 12-pounders. 



J3O4 Are there any more explosive substances than gunpowder f 



Yery many ; but all of them are too expensive or 

 dangerous for practical use. 



SO5 By whom was gunpowder supposed to have been discovered f 



It is generally agreed that gunpowder was used by 



