286

THEORT AND PRACTICE

TRACT S7.

Jx1l4xn«x20 17 3 x 30 , . , , J r

~ rr — — = 777—77 = 13 inches nearly, the depth ofpenetration.—But, as Mr. Robins found this penetration, byexperiment, to be only 5 inches ; it follows, either that histimber must have resisted more than twice as much as mine;

or, else, which is much more probable, that the defect in hispenetration resulted from the change of figure in his leadenball, from the blow against the wood ; as such bullets havebeen observed to be quite flatted by such a stroke.

157. Exam. 9. A one-pound ball, projected with a ve-locity of 1200 feet per second, having been found to pene-trate 15 inches deep into sound elm: It is proposed to ascer-tain the time of passing through every single inch of the 15,and the velocity lost at each of them ; supposing the resist-ance of the wood constant or uniform.—Here, the velocity vbeing 1200 feet, or 1200 x 12 = 14400 inches; and the ve-locities and times being as the square roots of the spaces, in

constant retarding forces, as well as in accelerating ones;2 x 15 30 1

and t being = ~ = ^ = iTo P art of a second >

the whole time of passing through the 15 inches; there-fore as

f