476 
ARTILLERY IN COAST DEFENCE. 
into the question, it will not give true results ; the instrument, set 
thus with a false height, would give corrections varying directly with 
the range ; while the tidal error varies inversely as the range and 
the powder error bears a fractional proportion to the range. 
The error in direction is best judged by eye, and if the Fire Com¬ 
mander’s station is at some distance to a flank of the guns, he must 
have an observer near them to estimate this error for him, who, of 
course, must be in communication with him. The angular error in 
direction can, of course, be measured by the arc of the depression 
range-finder if the observer is sufficiently well trained. It is much to 
be wished that a second depression range-finder for the purposes of 
observation should be mounted in each Fire Commander’s station; 
this would obviate the necessity for taking the other instrument away 
from its proper function of continuously recording the range. 
It facilitates the making of corrections if the tables are mounted on 
rollers; there should be one roller for Case II., having on it a tide 
table; a table of corrections to range for a time of firing of (usually) 
about three seconds; and a deflection table for the times of flight. A 
roller for Case I. requires no tide table; a table of range corrections 
for time of firing (usually) about eight seconds ; and a deflection table 
for times of flight plus two to four seconds for gun-layer to get clear 
of recoil. The tables should be so mounted on the roller that the 
corrections for a given range come one under the other. 
In this system of fire control the Fire Commander is entirely respon¬ 
sible for the correctness of the trajectory ; he has, therefore, to make 
the corrections and observe the results. It should be noted that the 
corrections will need constant watching; as the range changes, the 
tidal error may change, also the powder error; if the vessel alters her 
speed or changes her direction, the rate at which the range increases 
or decreases will vary, and so will the deflection correction. 
The Group Officer’s responsibility in this system, as regards fire 
control, is limited to choosing the proper moment to fire, and 
to making the proper correction for group difference; he has, of 
course, the responsibility of seeing that the guns are being correctly 
loaded and laid and at the right object, but this is part of the duties 
included under “ Fire Discipline/’ The Gun-Captains are also respon¬ 
sible that the guns are not fired, unless the laying has been properly 
completed within the prescribed time of firing, even though they 
receive the order from the Group Officer to commence firing. 
The third system of fire control is that used when we have an instru¬ 
ment which can tell us, not only the range to an object, but the position 
of the object with reference to the guns, that is the range and training 
necessary. The position-finder is such an instrument, and it auto¬ 
matically records, on dials at the group, the range and training to the 
object from the group by simply bringing the telescope of the 
instrument on to the object; thus the necessity for a group difference 
correction is done away with ; but there must be a separate instrument 
for each group. 
In this system the guns are laid, not on the object but on a spot 
over which it is about to pass, and fired when it comes over that spot. 
