FALLING BODIES. 
203 
it is 16.08 feet. In accordance with Hewton’s second 
law, the attraction of gravity on falling bodies is 
greater at the poles; on account of the flattening of 
the earth at the poles a body is nearer the center of 
the whole mass of the earth. 
Another experiment greatly surprised the class 
before whom we performed it. We laid a yardstick 
upon the table, one end projecting over the edge 
about four inches, the other end held down by several 
books. On the projecting end we laid a marble, and 
flve inches from it another. Then with a heavy ruler 
one of us struck a horizontal blow, which sent the 
second marble and the stick off in a horizontal direc¬ 
tion, allowing the flrst marble to fall to the floor. 
Both marbles left their position at the same instant. 
Although the second marble went through a hori¬ 
zontal space of flfteen feet, both struck the floor at 
the same instant. 
The conclusion was that gravity acts just as well 
upon objects when they have been set in motion by 
some other force as when they are allowed to drop. 
Accordingly, a cannon-ball flying through the air with 
a great velocity will descend to the earth the same 
distance per second as a freely falling ball. 
A ball thrown up into the air with a certain initial 
velocity will be as long in ascending as in descending, 
and will return with the same velocity with which it 
started, not taking into account, of course, the friction 
of the air. 
What is gravitation ? We say it is a force that 
belongs to all matter. All we know of it is that it is 
