68 
MINUTES OF PROCEEDINGS OF 
cent, of hits at 2000 metres, we have .. = 2-70; which, by the tables 
jO' lO 
which give the probability of striking, corresponds to 93 per cent, of 
hits, provided none of the shots are lost by lateral spread. It follows, 
therefore, that 7 per cent, of the shots will strike either too short or too 
long, and that the elevation may be considered sufficient if not more 
than 3 to 4 per cent, of them strike the parapet. 
Ex. 5.—The space between the first and second traverses of a line 
capable of being enfiladed has to be raked by means of enfilade fire 
from a short 15 c.m. B.L. gnn. The distance of the gun from the crest 
of the covering parapet is 1250 metres, that of the crest of the parapet 
from the crest of the first traverse 28 metres, and the horizontal distance 
of this crest from the foot of the second traverse 12 metres. The crests 
of the parapet and of the traverse are 4*5 metres above the terreplein, 
and the line joining the .centre of the guifis muzzle and the crest of the 
parapet makes an angle of 24' with the horizontal. 
If we take the mean point of impact at the foot of the second traverse 
we shall have 
tan a= = 0*375, 
I z 
and a = 20° 33 7 . 
In order to obtain an angle of descent of 20|° at the given distance 
we must employ a very small charge—say a little under 0*6 k.g. Since 
this charge gives unfavourable results, both as regards the action of 
the fuzes and. accuracy of fire, it appears more advantageous to take 
the mean point of impact higher—say 3*5 metres below the crest. 
We shall then have 
tan a = ^ = 0*29166. 
12 
The crest of the covering parapet, and therefore also that of the first 
traverse, is 1250 x tan 24' above the level of the muzzle of the gun. 
We have, therefore, 
tan n 1 = 
1250 tan 24' 
1250 + 28 
0*00683, 
and n x = 23 J', 
tan n 2 — 
1250 tan 24' — 3*5 
1250 + 28 + 12 
0*00405. 
By formula (1) we have 
tan y x = tan a + tan n 2 = 0*29166 + 0*00405 = 0*29571, 
and y 1 = 16° 28'. 
For a range of 1278 metres we find in the practice tables that the 
angle of descent (y^ would be 17° 55' with a charge of 0*7 k.g., and 
15° 8' with one of 0*8 k.g. 
