6 A VIS INERT I AE

these velocities; as also the different bodiesor quantities of matter in N° 4. require therespective forces to be impressed, or makethe respective resistances there mentioned,before they can be moved with the same com-mon celerity; in wha tever direction the mov-ing force is applied; whether upward ordownward (of which direction in particularmore by and by, N° 1 6.) backward or for-ward, obliquely or horizontally, in all posit"ble variety of directions.

VI. Moreover, all this is likewise certaintaken the contrary way, viz. from motionto rest; as far at least as experience reaches.For the body A, moving with a certain ve-locity as C, requires a certain degree of forceor resistance in an obstacle, to take off orstop that motion ; and moving with a velo-city as 2 C, or 2 A moving with a velocityas 1 C, it requires twice that force or strengthin an obstacle to stop the motion; andA moving with a velocity as 3 C, or 3 Amoving with the velocity 1 C, thrice the firstresistance only will bring it to rest, Q?c. AndA moving with the velocity ~ C, or t A mov-ing with the whole velocity C, one half the

first