64 
MIN.UTES OF PROCEEDINGS OF 
This angle is measured from the straight line connecting the centre 
of the gun's muzzle with the point of impact. The ground angle n 2 
has therefore to be found. The crest of the glacis lies above the level 
of the gun's muzzle by 909 m x tan 5' = 1’32 metres. The point of 
impact was fixed at 6 ra below the crest of the glacis; therefore 
y 2 = T32 m —- 6 m = — 4-68 m , 
4-A.Q 
and tan w 2 = — - -= — 0-004958, 
944 
— 17', 
and the above-mentioned angle of 9° 25' must be diminished by 17', 
giving 9° 8' as the angle of elevation for the lowest point of impact. 
Finally, to bring the mean point of impact to half the height of 
the scarp, the trajectory for 944 metres must be raised by l'25 m , which 
can be done by an addition of about 4'. The angle of elevation to 
be employed is therefore 9° 12'. 
We can arrange for the raising of the trajectory while determining 
the angle n 2 , by taking the point of impact at half the height of the 
scarp, by which 
,y 2 = 1-32 — 475 = -3-43, 
tan n Q — — = — 0 - 003634, 
944 
rto =13' (negative), 
and the angle of elevation = 9° 25' — 13' = 9° 12'. As the quadrant 
does not allow angles to be measured at less intervals than 2J', the 
angle of elevation must be taken at 9° 12^'. 
An interpolation of this kind would be unnecessary if the practice 
tables were, arranged for charges at intervals of 50 grammes; this, 
however, would make them too voluminous. Moreover, the method of 
proceeding which has here been given is excessively simple, correct 
enough for practical purposes, and (which is very important) gives in 
general rather too curved than too straight a path. If we were to 
take, in employing formula (1), the next larger charge (or the next 
smaller angle of descent) we should get a straighter path (Fig. 7). As 
the angle of elevation is calculated for the distance MD the trajec¬ 
tory would certainly pass through the point JD, but at the same time 
would strike the scarp above the intended point T. If we were to 
correct this error by decreasing the elevation the shots would impinge 
against the cover. If the trajectory is raised for half the 50 per cent. 
