Chap. 2. PHILOSOPHY:

55

from the laws of motion, answer most exactly to experience.A particular set os experiments has been invented to maketrial of these effects of percussion with the greatest exactness.But I must defer these experiments, till I have explained thenature of pendulums a . I ssiall therefore now proceed to de-scribe some of the appearances, which are caused in bodiesfrom the influence of the power of gravity united with thegeneral laws of motion ; among which the motion of thependulum will be included,

14.. The most simple of "these appearances is, when bo-ssies fall down merely by their weight. In this cafe the bodyincreases continually its velocity, during the whole time of itsfall, and that in the very fame proportion as the,time increas-es. For the power of gravity acts constantly on the body withthe fame degree of strength: and it has been observed abovein the first law of motion, that a body being once. in motionwill perpetually preserve that motion without the continuanceof any external influence upon it: therefore, after a body hasbeen once put in motion by the force of gravity, the bodywould continue that motion, though the power of gravityshould cease to act any farther upon it; but, if the power ofgravity continues still to draw the body down, fressi degreesof motion must continually be added to the body ; and the.power of gravity acting at all times with the seme strength,,equal degrees of motion will constantly be added in equalportions of time.

* These experiments are described in § 73.

15. This