TRACT 37.

OF GUNNERY-.

285

iron will penetrate into a block of elm, when dischargedwith a velocity of 1600 feet per second.

Here, because, by art. 139, the ball of 2 inches diameter,with 1200 feet velocity, penetrated 15 inches deep ; there-fore, by art. 141, the depth for the 24lb ball, or 5\55 inchesdiameter, with 1600 feet velocity, will be found by this pro-portion ; as 2 X 1200 1 : 5-5.5 x 1600 2 : 15 : ° 53 * 4> - ^— =

37 inches nearly, or 3 feet 1 inch, the penetration.

153. Exam. 6 . It is stated by Mr. Robins (vol. 1 , p. 273,of his works), that an 18-pounder ball, discharged with a ve-locity of 1200 feet per second, penetrated 34 inches intosound dry oak. It is required then to ascertain the com-parative strength or firmness of oak and elm.—By art. 140,the strength of the obstacle being as the diameter of the balland the square of the velocity directly, and the space pene-trated inversely; and the diameter of the 1 Sib ball being5-04 inches; we shall have,

/ _ rf " 2s _ 2 x 12 2 x 34 2 x 34 _ 17 _ t

F — — 5-04 x 12» x 15 ~ 5-04 x 15 — TiT 11Car ^'

Whence it would seem, that elm timber resists less than oak,in the ratio of about 17 to 19.

155. Exam. 7. A 24-pounder ball being discharged intoa bank of firm earth, with a velocity of 1300 feet per second,penetrated 15 feet. It is required then to ascertain the com-parative resistances of the earth and elm wood. Comparingthe numbers here with those of the 5th example with the

, „ . . / V*s _ 1S 3 x 15 x 12 256x 180 46080

same ball, it is — — —[ 3 ,- x37 — 133 * 3.7 — —

7* nearly. That is, elm timber resists about 7j- times more

than the earth.

156. Exam. 8 . To determine how far a leaden bullet,of of an inch diameter, will penetrate dry elm ; supposingit discharged with a velocity of 1700 feet per second, andthat the lead does not change its figure by the stroke againstthe wood.—Here d =£, n = i l-|-the specific gravity of lead,and n — 74 nearly, that of cast iron. Then, as before