472 
ARTILLERY IN COAST DEFENCE. 
of the day.” This error is beyond calculation, and can only be 
ascertained by observation of the results of the first shots; or, if 
time permits, a few trial shots may be fired at a known range. It 
should be pointed out, however, that the greater part of this error is 
due to a deficiency in muzzle velocity, arising from the age or differ¬ 
ence of brand of the powder; and that, therefore, the error will not be 
constant at all ranges. The table at page 310 “ Text-book of Gun¬ 
nery,” illustrates this well. It is there shown that with a 12-inch 
B.L. gun (muzzle velocity 1900) a loss in muzzle velocity of 50 f.s. 
would result in a loss in range of 50 yards at 1000 yards, and of 175 
yards at 4000 yards. Hence a trial shot from this gun, fired at a 
known range of 1000 yards, and falling 50 yards short, would in 
reality indicate that a correction of 175 yards was required at 4000 
yards. Again, the same table shows that half a gale of wind blowing 
up the range (towards the gun) would cause an error of one and-a- 
half yards (practically imperceptible) at 1000 yards, but at 4000 yards 
the error would be 32 yards. Thus it is evident that reliable informa¬ 
tion, as to the error of the day, can only be obtained by trial shots 
fired at a known range, if this range is somewhere about the same as 
that at which we are about to engage the enemy. It would usually 
be safe to give a + correction for the first shot, as powder rarely 
“ shoots up to the tangent scale.” 
When firing at a ship, a further correction must be made to carry 
the trajectory on to that part of the ship we wish to hit. This is 
necessary because, as mentioned before, guns are laid on the stem at 
the water-line (or stern at the water-line when the stem is not visible), 
and ranges are taken to the same points. If, therefore, no correction 
is made for length, a correctly laid salvo will all hit about the stem or 
stern, and some of the shots will certainly fall short and do no damage. 
We may wish to hit a definite point, as for instance, the forward bulk¬ 
head in a central citadel ship end-on at a short range, and in that 
case would find, in the list of ships, the distance of this point from 
the point aimed at; but if the length of range precluded any idea of 
attacking a particular point, we should add on about half the length 
of the ship, say 50 yards for battleships, so as to bring the trajectory 
on to the centre; if the ship makes a diagonal course with the line 
of fire, a less correction will be required. This correction will generally 
be an addition to the elevation, as we are generally laying at the 
nearest part of. the ship, and trying to hit a point further off. 1 When 
the ship is broadside-on, or nearly so, no correction to range is ordinarily 
necessary if using quadrant elevation ; but with tangent elevation 
usually a sufficient addition must be made to raise the point of impact 
a few feet, viz. : from the water-line which is the point aimed at, to 
half-way up the side. An exception would be in the attack of a water¬ 
line belt at close ranges, where with quadrant elevation some elevation 
may have to be taken off. 
So far the corrections that have been mentioned are equally applic- 
1 When the ship is retiring from the battery in a course which makes an angle of about 4 5°, or 
less, with the line of fire, her bows will be visible from the guns, and if that point is laid on, 
some elevation must be taken off* in order that the centre of the vessel may be struck. 
