GRAVITY. 



* 2 3 



fall to the earth's surface. In a teacup the spoon will attract air bubbles, 

 and large air bubbles will attract small ones, till we find a small mass of 

 bubbles formed in the centre of the cup of tea. Divide this bubble, and the 

 component parts will rush to the sides of the cup. This form of attraction 

 is illustrated by the accompanying diagrams. 



Fig. 14. 



Suppose two balls of equal magnitude, A and B (fig. 14). These being of 

 equal magnitude, attract each other with equal force, and will meet, if not 

 opposed, at a point (M) half-way between the two. But they do not meet, 

 because the attraction of the earth is greater than the attraction they rela-* 

 tively and collectively exercise towards each other. But if the size of the 

 balls be different, the attraction of the greater will be more evident, as shown 

 below, where the points of meeting are indicated respectively (figs. 1 5 and 16). 

 These experiments will illustrate the phenomena of falling bodies. Gravity is 

 the cause of this, because every object on the surface of the earth is very 

 much smaller than the earth itself, and therefore all bodies fall towards the 



Figs. 15 and 16. 



centre of the earth. A certain time is thus occupied, and we can find the 

 velocity or rapidity of a falling body very easily. On the earth a body, if 

 let fall, will pass through a space sixteen feet in the first second ; and as the 

 attraction of the earth still continues and is exercised upon a body already 

 in rapid motion, this rate of progress must be proportionately increased. 

 Just as when steam is kept up in an engine running down hill, the velocity 

 of the train will rapidly increase as it descends the gradient 



A body falling, then, descends sixteen feet in the first second, and for 

 every succeeding second it assumes a greater velocity. The distance the 

 body travels has been calculated, and the space it passes through has been 

 found to increase in proportion to tJte square of the time it takes to fall. For 

 instance, suppose you drop a stone from the top of a cliff to the beach, and 

 it occupies two seconds in falling, if you multiply 2x2, and the result by 

 sixteen, you will find how high the cliff is : in this (supposed) case it is 

 (omitting decimals) sixty-four feet high. The depth of a well can also be 

 ascertained in the same way, leaving out the effect of air resistance. 



