474 
ARTILLERY IN COAST DEFENCE. 
+ 
— 
+ 
— 
+ 
— 
Powder. 
50 
Tide . 
Length. 
50 
25 
Time of firing 
25 
_ / 
Nett Total + 50 
The nett result of the several corrections he will give to the dial 
number, who will show the range, as read by drum-reader, corrected 
by this amount. 
For instance, suppose the guns (9-incli R.M.L.) to be laid by quad¬ 
rant elevation; the tide to be low ; range 3000 yards; object, a 
battleship, approaching nearly end-on; and powder has been shoot¬ 
ing 50 yards short at this range. 
Then, the Fire Commander sees by his table that for low tide at 
3000 yards — 25 is the correction required, and enters it in the — 
column; for powder he enters 50 in the + column, and the same 
amount for length of ship; he now ascertains that the range is 
decreasing 50 yards in 20 seconds; looking to the “ time of firing ” 
table for case II., he sees that the correction is 25 yards, and, as the 
range is decreasing, this must be entered in the — column. The nett 
result of these corrections is + 50, which he, therefore, gives to the 
dial number, who, until a fresh correction is given him, will always 
show on his dial 50 yards more range than is read out by the drum- 
reader. 
The Fire Commander will also have to correct for deflection; for 
which three things have to be considered; first, if the wind is across 
the range, sufficient deflection must be given to counteract its effect; 
secondly, a correction must be made (except when the ship is end on 
to the guns) to carry the trajectory from the point aimed at (viz., the 
stem) to the point we wish to hit; these two corrections being neces¬ 
sary for stationary as well as moving objects. Lastly, correction must 
be made for the travel of the object during the time of flight. The 
actual distance travelled in this time is not of moment, the essential 
point to be ascertained is the arc traversed by the object. For 
instance, if a point moves through an arc of one degree in five seconds 
of time, and the time of flight is also five seconds, it is clear that we 
must lay the gun one degree ahead of that point in order to hit it; if 
the time of flight were 10 seconds, we should have to lay two degrees 
ahead ; and if two-and-a-half seconds, half a degree ahead, and so on. 
When the guns are laid by quadrant elevation the time of flight is all 
that need be considered, as the gun-layer standing on the sighting- 
step keeps his gun laid for direction until the moment of firing; when 
tangent elevation is used a small time of firing, to allow for the layer 
to get down from the slide, must be added to the times of flight. 
Thus there must be two tables, one for case I. and one for case II., as 
with the range correction. The time taken by the object to pass over 
