CORRECTIONS FOR QUICK TARGETS. 
125 
75 
Fig * 3> which, as is seen in Table I., corresponds to a range of 
2500 yards. Through B, draw B Q, parallel to PA, 
then B Q will represent the further boundary. Let the 
lines p/, pzpz, etc. cut B Q in the points a', b', etc., 
; then the channel will be divided into compartments, each 
corresponding to a certain range correction. 
It is, however, convenient to exhibit this information 
in another form. Draw A P and B Q, as before ( see 
Fig. 3) ; measure off, on Fig. 2, the distances G A, Ga, 
Gb, Gc , etc., and lay them off vertically, form A, in Fig. 
3, so that the points A', a i} b l} c 1} etc., are obtained. In a 
similar way, lay off on B Q, the proper distances from G, 
gi so that the points B', c./, etc., are obtained also. 
' Then if intermediate points are treated in like manner, 
the lines aal, bb', cc', etc., of Fig. 2, will become trans¬ 
formed into the curves 1 % a/, by, c Y c/, etc., of Fig. 3. 
cl Transfer the horizontal scale of yards, between A B in 
Fig. 2, to A' A', in Fig. 3; then the part of the figure 
below the last named line is no longer needed, and the 
V correction, due to any range, can at once be seen, if a 
, scale of yards, similar to that along G M, Fig. 2, be 
a i applied to A'P, A' Q, or any intermediate parallel line : 
B the zero of the scale being on the line A' A'. 
Now, it is suggested that in a channel, straight or 
nearly so, where variations of tide can be neglected, this 
method may be found useful. Local circumstances would 
A determine the limits, such as A P and B Q, in fig. 2, as 
also the useful values of v. Figures, similar to Fig. 3, 
might be constructed for each of these values, and 
disposed in a row of contiguous columns, each marked 
with its own velocity ; they then might be placed round 
the surface of a drum, rotating in a suitable cylinder, 
so that, through a slit in the latter, any desired column 
could be brought to view. On the outside cylinder a 
scale, reading ranges from G, should be placed verti¬ 
cally along the edge of the slit, which would show 
through what limits the various corrections held good. 
It would be constructed on the same principle as that 
A B below G M, in fig. 2. 
Thus Fig. 4 is a portion of the information, placed round a drum, 
constructed for forts commanding a channel/where the minimum range 
of an objective might vary from 800 to 2000 yards, the guns being 
9-inch, 10-inch, or 12*5-inch R.M.L., with an average “time of firing” 
of three seconds. 
Figure 5 gives a view of the outside cylinder when set for a ship 
steaming 22 knots ( v -- 11) along a line, that would give a minimum 
range of 1200 yards. 
1 These curves are rectangular hjperbolse; their equation is of the form Jc — v't, where v' is the 
variable value of the speed, resolved along any line P G, Fig. 1. 
