The motion which continues after the body has ceased to be in contact with the sensible impelling cause, is named continuous motion. The body impelled receives neither force nor motion from the impelling cause: neither force nor motion is anything transferrable or anything communicable; forcible velocity and change of place are but accidents of matter, and but local, casual circumstances of bodies. Being inert, the body cannot move itself. Motion, therefore, is but a physical effect, and must have a cause equal to the duration of the effect: motion after impulse has ceased, would be effect without cause—which is an absurdity and impossibility; therefore impulse is constant as motion, however insensible the impelling cause. These dynamic A body in motion is under unequal pressure on opposite sides, greater on the rear than front. The air in front resists, that in the rear may be said to recede from the body; therefore neither impels the projectile. Under such circumstances there remains but the alternative, that of the electric constitution of the body being changed by the previous impulse, by which medium of space accumulates on one side, or decreases on the opposite. The phenomenon admits of being thus illustrated: The first, previous or sensible impulse, effects de-electrisation of the body on the rear or side of impulse; influent medium of space immediately occupies the vacated rear, and by its pressure impels the body through the air. The velocity of the previous impulse, gives momentum to the body greater than the included freely-removable elementary matter can obtain; of consequence the latter is left behind in the air, and the pressure of the acquired medium of space in the rear, is the continuous impelling cause. Thus is the mistake of Dugald Stuart made evident, that "motion is the immediate and only effect of impulse." It is not the air's resistance which makes the motion of a projectile decline and end. Taking impulse as ten, resistance four, there remains six degrees of unresisted impulse, which should impel From the instant the body has ceased to be in contact with the sensible impelling cause, electric matter is re-entering the rear, which displaces gradually the impelling medium; and as are the increments of the former, so are the decrements of the latter, and so is the decline of motion. |