THE ROYAL ARTILLERY INSTITUTION. 
25 
10. The ranges recorded at Shoeburyness and which have formed the 
basis of the foregoing Tables, are subjected to two operations. 
(a) Having found the arithmetical mean of all the ranges for a given 
elevation, the deviation of each individual range from this mean is taken out, 
and the average of these differences, without regard to sign, is called the 
mean difference of range . 
iff) Each shot is referred to a datum line for deflection ; the mean of all 
the deviations from this line, taken with regard to sign, is the true mean 
direction of all the shots, as referred to the datum. This quantity again, 
being subtracted from each observed deflection, the remainder is the deflection 
of the shot as referred to the mean direction of the whole, and the average 
of these remainders, taken without regard to sign, is the true mean deflection 
of the series after eliminating wind, derivation as our neighbours call it, or 
drift, and any other constant error, such as want of verticality in the tangent 
sight. It correspondes in fact to the figure of mirit in rifle practice. 
I subjoin an extract of these quantities for various series of practice, 
taking the results at 2°, 5°, and 10° as a criterion of the whole. It so 
happens that up to the present time the 40-pr. has been fired less frequently 
than the other guns under circumstances giving a mean of 10 or more exactly 
comparable shots at 10°. Less than 10 rounds will give a very reliable 
mean range, but not so reliable a difference of range, or mean deflection. 
Table YL 
MEAN DIFFERENCES OF RANGE AND MEAN DEFLECTIONS OF ARMSTRONG GENS 
OBSERVED ON CERTAIN OCCASIONS OF EXPERIMENTAL PRACTICE, WITH THE 
MEAN RANGE TO WHICH THEY BELONG. 
Date. 
2 ° 
5° 
10 ° 
[ No. of 
rounds. 
Mean 
range. 
Mean 
differ. 
of 
range. 
Mean 
Deflection. 
o! 
^ g 
Mean 
range. 
Mean 
differ. 
of 
range. 
Mean 
Deflection. 
d! 
s 
Mean 
range. 
Mean 
differ. 
of 
range. 
Mean 
Deflection. 
yds. 
yds. 
yds. 
yds. 
yds. 
yds. 
yds. 
yds. 
yds. 
9-pr. Charge, 1 lb, 2 oz. 
4/ 1/62 ! 20 | 
820 | 19-7 | 0-77 | 
20 | 1821 | 20*2 | 1*57 | 20 | 2980 | 26*0 | 3*371 
12 -pr. 
Charge, 1 lb. 8 oz. 
25/ 2/61 
20 
988 
12*9 
0*37 
20 
2006 
11*4 
0*60 
20 
3249 
22*5 
4*46 
20/10/61 
— 
-- 
— 
— 
10 
2019 
25*8 
1*00 
10 
3304 
31*9 
1*80 
3/12/61 
10 
1089 
10*3 
0*50 
10 
2081 
11*7 
1*10 
10 
3399 
24*2 
0*80 
99 
10 
1101 
12*4 
0*60 
10 
2111 
12*3 
1*40 
10 
3418 
18*1 
0*90 
6 / 1/62 
20 
1102 
18*1 
0*55 
20 
2116 
12*8 
1*20 
20 
3480 
21*3 
2-40 
L. 1 
3. 20-pr 
>. Cl 
large, 2 lbs. 8 c 
>z. 
6/12/61 
110 
| 810 
1 9 '° 1 
0-50 
1 10 1 
[ 1595 1 
33*5 1 
| 1*50 I 
9 | 
2368 I 
24*8 1 
1*10 
6/12/61 
1 10 
| 810 
1 5*7 | 
0-30 
1 10 1 
1600 1 
45*3 1 
| 0-60 [ 
-1 
“ 1 
~ 1 
— 
[VOL. III.] 4 
