72 Journal of the Mitchell Society [^August 



first will just be lifted bj the same steam pressure at the equator. 



(11) Another simple illustration will be given. The work 

 of raising a body of weight W lbs. at sea level, at latitude 45°, 

 h feet, is (W^) ft. lbs. At this place, call the acceleration due 

 to gravity g, at a second place g^ ; whence the attraction of the 

 earth on the same body at the second place is by ( 1 ) 



9i 

 Wi= — W 



9 



Hence the work of lifting it, at the second place, is, in ft. lbs., 



9i 

 W^h = —{Wh) 



9 



(12) MASS. Mass of a body means the quantity of matter 

 in the body, which is not supposed to alter in amount by chang- 

 ing the position of the body relative to the earth or to be affected 

 by the expansion or contraction of the body. Body here refers 

 to a limited portion of a gas or liquid or any solid body. 



jN^ow by the experimental law, eq. (1) the ratio W/^ of the 

 weight of the body, as given by a spring balance, to the 

 acceleration due to gravity at any point within the sphere of 

 the earth's attraction, is constant. Hence mass, which is like- 

 wise unalterable by a change of place, is proportioned to W/g. 

 In the engineers' system it is usual to write for the mass irij 

 the equality, 



W 



m = — (3) 



9 



so that, in this system, W^g can be regarded as the measure of 

 the mass. For the same place, it varies directly with the 

 weight. 



We have now a precise measure of mass and can appreciate 

 what properties of matter the word mass includes. 



(13) The term "density" can now be defined as the quotient 

 of mass by volume. 



