CORRECTIONS FOR QUICK TARGETS. 
13 
to be moving parallel to G L, its angular velocity with respect to G is, 
in circular measure, 
v cos P G 31 
WP 
which, in degree measure is, 
180 x 60 v cos PGM . 
— --?Tt 5 -minutes, 
7r Uri 
or 3420 v cos P G M . 
1 ^ -p * approximately. 
Now, if R be the range in yards, and t' the time of flight in seconds, 
when using Case II., or the time of flight plus some constant, when 
using Case I., and D the correct deflection in minutes for any given 
position of P, then, ^ 
D = 8420 v cos P G M x t . (3) 
If, now, we take any unit of deflection, say 15', we can, from 
equations similar to (3), determine through what limits any given value 
of D will hold good. 
For example, we might give D the successive values of 74', 224', 
374', 424', etc., and in each case determine the value of the angle 
PGM , for the requisite values of v. The factor can, of course, be 
obtained from the range table and the conditions of firing; thus, with 
the 9-inch R.M.L. and Case II., it will be found to vary from 350 to 
450 as the range changes from 5000 to 900 yards. 
In this way Table VII has been compiled. 
The graphic method can then be applied. 
Divide G L and G M into scales of equal parts, to read yards (Fig. 7) 
and, as an example, let v = 8. Draw quadrants of radii 1000, 2000, 
3000, etc., and mark off on them the angular limits as given in the 
table; join the points so found, and the water-way is divided into 
regions over which certain deflections hold good. Draw A P and 
B Q to represent a channel, whose perpendicular distance from the 
gun varies from 800 to 2000, say; we see, in the figure, it is divided 
into strips, in the same way as the channel of Fig. 3. Then, proceed¬ 
ing as in the case of Fig. 3 and Fig. 4, the deflection information can 
be set forth for each velocity in contiguous columns, to which vertical 
scales reading ranges can be applied. The scale employed is that on 
GLoy GM (fig. 8). 
Fig. 9 is a portion of the information placed round a drum, con¬ 
structed for forts commanding a channel, when the minimum range of 
an objective might vary from 800 to 2000 yards. When a channel 
is not very wide, and four or five velocities are considered sufficient, 
columns of corrections for range and deflection can be disposed round 
the same drum, and arranged so that when the latter is clamped the 
two sets of corrections are simultaneously visible, at two slits or open¬ 
ings, on opposite sides of the cylinder. 
Certain channels lend themselves to the selection of points or spots 
for concentration of fire on torpedo boats or fast cruisers; the above 
