70 Journal of the Mitchell Society [August 



body varies both with the latitude and altitude, it is evident 

 that the equal armed balance does not indicate, everywhere, the 

 attractive force of the earth on the body. 



The same remark applies to any lever balance or platform 

 scales. 



(5) Suppose a spring balance to be graduated with a set of 

 standard British weights at sea level at latitude 45° where 

 g = 32.174 ft. pr. sec. pr. sec. is the acceleration due to gravity. 

 'Now suppose a certain body there, when hung from the spring 

 balance, to depress the pointer until it reads W lbs., then the 

 attraction of the earth, at this point, for the body is exactly 

 W pounds force. 



Similarly, if the body is hung from this same "standard" 

 spring balance at any other point on the earth, although the 

 pointer may not read the same as before, still it indicates ex- 

 actly the force with which the body is attracted by the earth at 

 the place. This is the true weight of, or the pull of the earth 

 on, the body and is the only one to be considered where great 

 scientific accuracy is required. 



(6) Call the weight of the body at the second place Wj and 

 the acceleration due to gravity g^ ft. pr. sec. pr. sec. ; then since 

 it is an Experimental Fact that weight varies with acceleration, 



Wi W 



- = - (1) 



9i 9 

 This simple equation gives the solution to a number of prob- 

 lems involving weights at different latitudes. 



(7) Thus, if the standard spring balance has been graduated 

 at sea level at latitude 45° and a body weighs there W pounds, 

 it will weigh at the equator, at sea level, where g ■==-- 32.0894, 



32.0894 



Wi W== 0.99737 W (lbs.) 



32.174 



If W = 10000 lbs., Wi-= 9973.7 lbs., a difference of only 26.3 

 lbs. in 10000 ; so that for ordinary commercial or engineering 

 purposes the difference is negligible. It is to be noted that the 



