61 
THE ROYAL ARTILLERY INSTITUTION. 
1. If formula (1) is employed, we have 
tan y 1 = tan a + tan n 2 = 0-2087 + 0'0069 = 0-2156, 
7l = 12 ° 10 '. 
In the practice tables of the short 15 c.m. breech-loading gun we 
find for a distance of 1200 metres and an angle of descent of 12° 10' 
a charge of 0*9 kilogrammes; and as the final velocity, which is given 
as 164*4 metres, may be looked upon as sufficient, this charge may be 
employed. 
In the corresponding column of this table the angle of elevation is 
given as 11° 25'; therefore the angle of elevation corresponding to 
the lowest point of impact will be 11° 25'+ 41'= 12° 6'. 
With this elevation half of the shots would strike the glacis; the 
vertical spread is given as 3*45 metres, and its half is therefore 
1*73 metres. In the next column we find that 5' more elevation move 
the point of impact 1*72 metres higher; we must therefore further 
increase the elevation by 5', making it 12° 11'. 
2. If formula (2) is employed, we have 
tan y 2 = tan a + tan ; and, since tan 41'= 0-0119, 
tan y 4 = 0*2087 + 0*0119 = 0*2206, 
y 2 = 11° 27'. 
Though the distance x 2 (= 1228 metres) is not exactly given in the 
tables it is still to be inferred that the required angle of descent 
can be obtained between 1200 and 1300 metres with a charge of 
0*9 kilogrammes; and we find by interpolation, 
And since 
Angle of descent for 1300 metres = 13 22 
„ „ 1200 u =12 10 
Difference . 1 12 
100 : 28 :: 1° 12': a?, 
by which x = 0*72 X 28'= 20', 
we shall have the angle of descent for 1228 metres = 12° 10' + 20' 
= 12° 30', which is only slightly larger than the required one of 
12° 27'; consequently, the charge of 0*9 k.g. is to be regarded as the 
correct one. 
Since the elevation for 1228 metres is not given in the table, we 
interpolate. 
or 
Angle of elevation for 1300 metres = 12 31 
1200 „ =11 25 
Difference . 
100 : 28 :: 1° 6': x, 
x = 0*66 x 28 = 18'. 
1 6 
