7(5 



WELLS'S NATURAL PHILOSOPHY. 



upon a particular spot in the distance ; thus producing a 

 desired effect without a wasteful expenditure of ammuni- 

 tion. 



Fig. 48. 



Fig. 48 represents a bombardment, and the three lines indicate the curves 

 made by the balls. If the bombardment had been conducted from an eleva- 

 tion, instead of the level surface, the balls would have gone beyond the city, 

 ns shown by the familiar fact, that we can throw a heavy body to a greater 

 distance from an elevation, as the steep bank of a river, than on a plain, or 

 level ground. It was on this principle that Napoleon bombarded Cadiz, at the 

 distance of five miles, and from a greater elevation, the balls could have been 

 thrown to a still greater distance.* 



* The following facts respecting the explosive force of gunpowder, and its application to 

 projectiles, will be found interesting and instructive in this connection. The estimated 

 force of gunpowder when exploded, is at least 14,750 pounds upon every square inch of 

 the surface which confines it. Count Runiford showed, by his experiments made about 

 60 years ago, that if the powder were placed in a close cavity, and the cayity two thirds 

 filled, its dimensions being at the same time restricted, the force of ezplosioa would ex- 

 ceed 150,000 pounds upon the square inch. 



The force of gunpowder depends upon the fact, that when brought in contact with any 

 Ignited substance, it explodes with great violence. A vast quantity of r?as, or elastic Jluid, 

 is emitted, the midden production of which, at a high temperature, is the cause of the 

 Tiolent effects which are produced. 



The reason that gunpowder is manufactured in little grains, is that it may explode moro 

 quickly, by facilitating the passage of the flame among the particles. In the form of dust, 

 the particles would be too compact. 



The velocity of balls impelled by gunpowder from a musket with a common charge, has 

 been estimated at about 1,650 feet in a second of time, when first discharged. The utmost 

 Velocity that can be given to a cannon-ball is 2,000 feet per second, and this only at th« 

 moment of its leaving the gun. 



In order to increase the velocity from 1,650 to 2,000 feet, one half more powder is re- 

 quired ; and even then, at a long shot, no advantage is gained, since, at the distance of 

 500 yards, the grea. 'it velocity that can be obtained is only 1,200 or 1,300 feet per second. 

 Great charges of powde. ■^re, therefore, not only useless, but dangerous ; for, though they 

 give little additional force to 'he ball, they hazard the lives of many by their liability to 

 burst the gun. The velocity is greater with long than with short guns, because the influ- 

 ence of the powder upon the ball is longer continued. 



The essential properties of a gun are to confine the elastic fluid generated by the explo- 

 sion pf the powder aa completely as possible, and to direct the course of the ball in a 



