## Rifles and rifle practice; an elementary treatise upon the theory of rifle firing, explaining the causes of inaccuracy of fire, and the manner of correcting it ...

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1861 Excerpt: ...with the grooves, this needle also turns, and measures the arc, which enables us to read the turn, or twist of the grooves. To calculate the initial velocity of a projectile.--The initial velocity of a ball is the velocity with which it leaves the muzzle of the piece: this velocity can be calculated by means of a revolving machine. Two vertical disks (Fig. 24), through which a horizontal axis is passed, are separated by an interval of nine feet. A motion of rotation is imparted by means of an endless rope. This motion becomes uniform after a few revolutions, a dozen, for example. Fire the arm horizontally in the vertical plane of the axis of the machine, and as near as possible to the first disk. The ball pierces the first disk, and takes a certain time to reach the second. The point where the ball pierces the second disk is at a greater distance from the vertical as the motion of rotation is the more rapid. To find the velocity the ball had in passing through the space separating the two disks.--Suppose that the machine makes eight revolutions in one second, and that the distance between the disks is nine feet, the time of 1" one revolution would be--=0.125". Suppose the ball to have struck the first disk at 0, and the second at V, the angle at the centre A, for example, 30; it would appear that the second disk had revolved through a circular space of 30, while the ball was passing from the first to the second disk. It is evident that if this circular space had been 360, the time taken by the ball to pass from the first to the second disk would be 0.125"; but the circular space being only 30, the time that the ball takes to pass over the interval of nine feet will be found in the following manner: If the circular space be 360, the time is 0....

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