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lightly treated, or omitted altogether, this has notbeen done without a purpose.
It had been recognized long before Newton’s timethat this globe on which we live possesses a powerof drawing to itself objects left unsupported at anydistance above the earth’s surface. It is, indeed,very common to find the recognition of this factascribed to Newton, who is popularly supposed tohave asked himself why a certain apple fell in hisorchard. But the fact was thoroughly recognized longbefore his time. Galileo , Newton’s great predecessor,had instituted a series of researches into the law ofthis terrestrial attraction. He had found that allbodies are equally affected by it, so far as his experi-mental inquiries extended; and he established theimportant law that the velocity communicated to fall-ing bodies by the earth’s attraction increases uniformlywith the time of falling; so that whatever velocity isacquired at the end of one second, a twofold velocityis acquired at the end of the next, a triple velocity atthe end of the third, and so on.
In order to estimate the actual velocity whichgravity communicates to falling bodies, Galileo causedbodies to descend slightly inclined planes. He showedthat the action of gravity was diminished in the pro-portion which the height of the plane’s summit bearsto the sloped face; and by making the slope veryslight, he caused the velocity acquired in any givenshort time to be correspondingly reduced. To reducefriction as much as possible, he mounted the descend-