46 



Domestic Science 



cubic inch of lead be placed in the pan, the spring will 

 lengthen to a certain extent, and this length may be 

 noted by marking the distance a metal indicator con- 

 nected with the lower end of the spring moves along a 

 vertical scale attached to the ring. If a second cube of 

 lead, similar in all respects to 

 the first, be now placed in the 

 pan, the further increase in 

 length of the spring will be 

 found to be equivalent to that 

 first noted. That is to say, the 

 pull of the Earth on two cubic 

 inches of lead is twice as great 

 as its pull on one cubic inch. 

 Three cubes will cause three 

 times the elongation produced 

 by one cube, four cubes four 

 times, and so on. Each cube 

 contains the same quantity of 

 matter, i.e. has the same mass, 

 an'd hence we see that the force 

 exerted between the Earth and 

 any given body is proportional 

 to the mass of the latter a 

 body of twice the mass of 

 another being pulled twice as 

 hard towards the Earth's sur- 

 face, one of ten times the mass 

 ten times as strongly, and so on. 



The pull exerted by the Earth upon a body in virtue 

 of its mass is called its " weight ", and the above 

 experiment shows that, at any given point on the 

 Earth's surface, the weight of a body is proportional 

 to its mass, and vice versa. 



Fig. 18. 



