294 M. Carnot's Theory of Defence 



with blindages, as M. Carnot imagines ; for a strong cap or hat, 

 and a cover of thick leather for the back and shoulders, would 

 be sufficient protection from the effects of his vertical fire with 

 small balls, 



" As the quantity of balls required to feed mortars discharging 

 600 balls at a time would be very considerable, M. Carnot ob- 

 serves that cubes of iron, of 8 or 10 lines side, cut from square 

 bars of this dimension, may be substituted. These, he says, 

 may be fired from mortars, howitzers, or stone-mortars, and 

 will produce the same effect as balls (page 491, Carnot.) 

 " Let us consider this : 



10 lines French are equal to -89523 inch English. 



The coiitent of the cube is -71746 



Its weight is 3-082'2 ounces. 



" Now take a ball of the same weight : 



Its diameter is Mil inches. 



Its terminal velocity is 185 feet per sec. 



Its potential altitude is 534 feet. 



" We have no experiments from which we can ascertain the 

 terminal velocity of square shot ; but from comparative expe- 

 riments with round and flat surfaces, we know that the resist- 

 ance of the air to the flat end of a Cylinder is more than double 

 the resistance to a ball of the same diameter. Thus, although 

 the urging force of a ball and cube of the same weight be the 

 same, yet the surfaces upon which the resistance acts (and very 

 irregularly in regard to the cube) are very different : 



The surface of the ball is 3-87045 



the cube is 4-80862 



" From this, together with what has been said respecting the 

 descent of balls, we know, and that is enough for our present 

 purpose, that the terminal velocity of the cube must be much 

 less than 185 feet per second ; and, consequendy, its effect or 

 momentum inferior to that of a 3-08 ounce-ball. The motion of 

 a cubical shot will, besides, be quite irregular, descending 

 sometimes with an angle, then a face, then an edge foremost. 



