27S OUTLINES OF NATURAL PHILOSOPHY. 



It may be shewn by this, that a ball 1.05 lb., dis- 

 charged with a velocity of 2000 feet, will ascend 

 only to the height of 2920 feet, or little more than 

 half a mile, whereas in vacuo it would have ascend- 

 ed to the height of eleven miles and three-fourths. 

 HUTTON, ibid. p. 284. 



374. If a body descending in the atmosphere, 

 has acquired such a velocity, that the resistance is 

 equal to its weight, the accelerating and retarding 

 forces being equal, its motion will become uni- 

 form. 



Hence, since .5286 d 5 is the weight of an iron ball of 

 the diameter d, if we make 



523.6 d ZJ-L v, we have a quadratic equation, 

 oOO 



from the solution of which v may be found. The 

 velocity thus found is called the terminal velocity of 

 the falling body, or of the projectile. For an iron 

 ball of 1 lb., the terminal velocity is 244 feet ; for 

 one of 42 lb., it is 456. Vid. TABLE, BUTTON'S 

 Course, vol. in. p. 291. 



In strictness this velocity is not acquired till after an 

 infinite time, and a descent infinitely long: the 



time 



