THE ROYAL ARTILLERY INSTITUTION. 
445 
In addition to tlie above table, a small table of the mean quadratic 
deflection is required; that is, the mean lateral and the mean vertical 
deflections are assumed to be identical.* 
C. 
Mean quadratic deflection and amount by which the height of the mean 
point to be struck in breaching should be diminished . 
12-pr. Steel Gun. 
Distance in yds. 
Charges. 
2-48 lbs. 
1-8 lbs. 
1*13 lbs. 
0*68 lbs. 
ft. 
ft. 
ft. 
ft. 
233 
0-3 
0-3 
0-2 
0-6 
467 
0-8 
0-8 
0-6 
3-5 
700 
1-4 
1-4 
1*4 
8-5 
933 
2-2 
2-3 
2-9 
14-0 
1167 
3-3 
3-9 
6-1 
20-0 
1400 
4-7 
7-1 
12-2 
— 
1633 
6-5 
13-2 
21*9 
— 
With a series of tables such as above described, the gunner can 
easily find an answer to the problem proposed at the beginning of this 
paper. 
The Eussian formula is as follows :=~ 
tan 6 = 
A — a 
(h ± H) =p H 
where A — horizontal range in feet up to face of wall, 
a = horizontal range in feet up to crest of covering work, 
h = height of crest of covering work above muzzle of gun, 
II = height or depth of point to be struck on the face of the 
wall to be breached, above or below the horizontal line 
through the muzzle of the gun. 
The upper signs in the formula are to be used when the point to be 
struck is below the horizontal line through the muzzle of the gun ; the 
lower signs when the point to be struck is above the horizontal line 
through the muzzle of the gun. 
* This assumption, if assumption it be, though perhaps not absolutely correct, seems to be 
sufficiently- so for all practical purposes. See Helie, “ Traite de Balistique Experimental,” Paris, 
1865, p. 600, The Russian tables show them to be alike, or very nearly alike, up to 1200 yds. 
range. 
