260 LIGHT SCIENCE FOR LEISURE HOURS. 



this parabola, and to deduce the range from the initial 

 velocity according to some simple principles deduced 

 from the properties of the curve. All this is founded 

 on a complete misapprehension of the true difficulties 

 in the way of the problem. Only projectiles thrown 

 with small velocity from the earth travel in parabolic 

 paths. A cannon-ball follows a wholly difierent kind 

 of curve. The resistance of the air, which seems to 

 most persons a wholly insignificant item in the in- 

 quiry, is so enormous in the case of a cannon-ball as to 

 become* by far the most important difficulty in the 

 way of the practical artillerist. "When a 250-pound 

 shot is hurled with such force from a gun as to cover a 

 range of six miles, the resistance of the air is about 

 forty times the weight of the ball that is, is equiva- 

 lent to a weight of upward of four tons. The range 

 Is such a case as this is but a small fraction of that 

 which would be given by the ordinary parabolic 

 theory. 



As regards artillery practice in war, there are other 

 difficulties in the attainment of a very extended range. 

 Cannon meant for battering down forts cannot possibly 

 be used in the same way that "Whitworth's was used 

 at Shoeburyness. If the shot flung from this gun at 

 an elevation of thirty-three degrees could have been 

 watched, it would have been found that it fell to the 

 earth at a much greater angle that, is, much more 

 nearly in a perpendicular direction. On the ordinary 



