yes

theory and practice

TRACT 37.

ing at the requisite quantity of elevation in the piece, to hita distant object, the practitioner might be supplied with cer-tain easy and practical rules, for making that allowance ofelevation.

104. Thus then, suppose the mark or object b, at thehorizontal distance ab, from the gun at a. Now suppose,first, that the ball is discharged in the horizontal directionAB, in which case the gun is said to be laid, and the shot firedpoint-blank, and is supposed to proceed a considerable wayin that direction; yet the ball constantly descends from the"horizontal line from the very beginning of the motion,though for a considerable space the descent is so little as tohe hardly perceptible. For, in fact, as soon as ever the shot•issues from the piece, it is deflected below its direction by theforce of gravity, and that more and more rapidly, the longerit is in motion, in proportion as the square of the time. Sothat the point-blank shot is to be considered only so far as tillthe descent from the horizontal line, or the angle bac canbe practically observed ; or, while that angle is so small, bythe curve line ac deviating so little from the right line ab,that the difference may beneglected, withoutany considerableerror. But in cases in which the space and time ol flight areso considerable as to deflect the shot in the curve line Ac, tothe depth of isc below the intended object n, then in practicethe gun must be pointed in the direction ad, at a mark n, asmuch above a as c is below b ; for then taking the curvedpath ab, it may arrive at the object b. We are therefore toconsider the projectile in the direction of the right line ad,and find bow far it will sink below that line at the point d ;which will be very easy, if the time of moving from a to nor B be known, for the line DB will be described by the ac-