74 Journal of the Mitchell Society '[August 



(18) In formula (5) above, W is supposed to be the weight 

 of the body in pounds as determined by a standard spring bal- 

 ance, used at the place of the body. By formula (1), W can be 

 taken as the weight by spring balance at 45° latitude, provided 

 g is put = 32.174. But W will be the same if the body is 

 weighed on an equal armed balance anywhere (4) ; hence, sup- 

 posing the body weighed in the usual way on a lever balance, 

 formula (5) can be written in the exact form, 



W 



F = a (6) 



32.174 



This is evidently the most practical form of equation (5). 



(19) BEITISH ABSOLUTE SYSTEM. In the British 

 engineers' system, with which we have dealt so far, the pound 

 weight at sea level at latitude 45° has been taken as the unit of 

 force and the unit mass is derived from the equation 



W 



m = = 1 ; 



32.174 

 whence the unit mass is the mass of a body weighing 32.174 lbs. 

 on a standard spring balance at sea level, at 45° latitude, or on 

 a lever balance any^vhere. In the British absolute system the 

 mass of the piece of metal, called a pound weight, is taken as the 

 unit of mass, and the unit of force is defined as that force which, 

 acting for one second on the mass of the pound piece of metal 

 generates in it a velocity of one foot per second. 



From numerous experiments it is known that if a body weigh- 

 ing one pound, on a lever balance, fall freely for one second, 

 at sea level, at latitude 45°, it will acquire a velocity of 

 g = 32.174 feet per second. The force acting on the body is 



1 

 1 pound. If this force was — of a pound, the body at the end 



9 

 of one second, would have a velocity of one foot per second. 



1 

 Hence the unit of force, at the place, is — of a pound (force) 



9 



