| (91) sin 2φ = 2C | [ | I(V) - | ΔA | ] | , | ||
| ΔS |
| (92) sin 2β = 2C | [ | ΔA | - I(v) | ] | . | ||
| ΔS |
To simplify the work, so as to look out the value of sin 2φ without the intermediate calculation of the remaining velocity v, a double-entry table has been devised by Captain Braccialini Scipione
(Problemi del Tiro, Roma, 1883), and adapted to yd., ft., in. and lb units by A. G. Hadcock, late R.A., and published in the Proc. R.A. Institution, 1898, and in Gunnery Tables, 1898.
In this table
(93) sin 2φ = Ca,
where a is a function tabulated for the two arguments, V the initial velocity, and R/C the reduced range in yards.
The table is too long for insertion here. The results for φ and β, as calculated for the range tables above, are also given there for comparison.
Drift.—An elongated shot fired from a rifled gun does not move in a vertical plane, but as if the mean plane of the trajectory was inclined to the true vertical at a small angle, 2° or 3°; so that the shot will hit the mark aimed at if the back sight is tilted to the vertical at this angle δ, called the permanent angle of deflection (see Sights).
This effect is called drift and the reason of it is not yet understood very clearly.