50 
MINUTES OE PROCEEDINGS OE 
1869, gained very valuable experience in curved breaching fire which 
bore fruit at the siege of Strasburg, and which, more recently, has been 
enlarged by the experiments at Grraudenz in 1873. 
The French artillery, too, in the year 1863, carried out experiments 
in curved fire against Fort Liedot in the island of Aix. 
Though the results obtained at the above-mentioned siege cor¬ 
responded to the expectations entertained, still it should not escape 
notice that in this case the circumstances attending the employment of 
this kind of fire, especially as regarded the nature of the profiles, 
were peculiarly favourable. In the case of the more modern fortresses 
—which have been planned, defiladed, and furnished with traverses 
with due regard to the peculiarities of breech-loading rifled guns—the 
employment of curved fire will be attended with far greater difficulty. 
2. Ascertaining the Angle oe Descent. 
Supposing the covering mass to be nearer the object than the gun, 
if we imagine a parabola to be drawn through the following three 
points, viz. the centre of the muzzle of the gun, the highest point of 
the cover, and the point to be struck, it is evident that the small 
portion of this parabola which lies between the cover and the object of 
fire will very nearly coincide with the actual path of the shot through 
these points, and that, consequently, we shall be in a position to cal¬ 
culate the angle of descent, either at the top of the cover or at the point 
to be struck, by the properties of the parabola. If one of these angles 
and the range are known we can get the charge and elevation from the 
accompanying practice tables, either directly or by interpolation. 
The formulas to be employed in the determination of these angles of 
descent, the derivation of which is given in Section 4, Part 1, of the 
“ Handbook for the Lit. Artillery,” are :— 
For calculating the angle of descent at the highest point of the 
cover (Fig. 1), 
tan yj = tan a + tan ...(1) 
and for calculating the angle of descent at the point of impact, 
tan y 2 = tan a + tan n x ; .(2) 
in which the angles of descent are always measured from the line con¬ 
necting the centre of the gun-muzzle and the point to be struck—in 
formula (1) from the line ML, in formula (2) from the line MT. 
Fig . 1. 
