28 
PRINCIPLES OE GUNNERY. 
on the side of the slope AB, GKO the trajectory, or path of the pro¬ 
jectile in the air, GV a tangent to the trajectory at the muzzle; then 
GV represents the line of fire, GO the line of sight. 
Suppose POT a tangent to the trajectory at 0 , the point of impact, 
GAT a horizontal line; then YGO is the angle of departure, PTG the 
angle of descent, VGD the angle of fire.* 
Range. The range is the distance from the muzzle of the gun to the 
second intersection of the trajectory with the line of sight. The range 
is not accurately the distance to the point at which the projectile 
impinges on the plane, unless that is also the point aimed at; but the 
difference is practically of importance only at short distances.f 
0 is the point aimed at, STO the line of sight, MPO the trajectory, 
TO the range. 
In practice, the range is often taken as the distance from the muzzle 
of the gun to the first point of impact of the projectile upon the 
ground; and unless there are great differences in level, it is sufficiently 
accurate for ordinary purposes. 
Terms dis- The terms distinguishing the various natures of artillery fire have 
the g ?aSouf reference (1) to the conditions within the vertical plane, or plane of 
S?tmery 0f fi re i (2) to the conditions within the horizontal or ground plane. 
fire. 
(1) The terms denoting the conditions within the vertical plane, or 
plane of fire, are direct fire, indirect or curved fire, and high-angle fire. 
Direct fire. Direct fire is the fire from guns with service charges at all angles of 
elevation not exceeding 15°. 
inciirector Indirect or curved fire is the fire from guns with reduced charges, and 
curvedfiie.^^^ howitzers and mortars at all angles of elevation not exceeding 15°. 
High-angie High-angle fire is the fire from guns, howitzers, and mortars at all 
hie ' angles of elevation exceeding 15°. J 
(2) The terms denoting the conditions within the horizontal or 
* In the above figure it has been thought simpler to neglect the consideration of the small 
perpendicular distance between the axis of the bore and the top of the fore, sight, 
f Vide “Proceedings, R.A. Institution,” Vol. III. p. 27. 
X Vide Regimental Oder dated D.-A.-G.’s Office, 31st .January, 1877. 
