1^ A IN JL» 
JXViU iVV A X Jl, rt 
V ixuc u, xa^ij. 
ftad can be mado to operate a transmitter, so that the in- 
stantaneous rate, when ascertained as above, can be trans- 
mitted to the pin ■« where the orders to raise or lower the 
eights at the speed required are being given. 
Note with regard to both these instruments that they 
indicate the rate at the moment, that they must be pointed 
at the target, and must be kept in coincidence with the 
course line. Neither can give a continuous indication of a 
A can now continue firing with confidence so long as its 
position is not altered; but if A proceeds to start at a high 
i-'-"''''" V- 
7^ 
7 
A E 
%a. 
changing rate, neither can be used when the firing ship is 
turning. Both require the target to be visible. Let us see 
how these limitations affect the Dardanelles problem. 
Our ships there are engaged in two tasks — to support 
the infantry in their advance to the GaUipoli heights and 
to destroy the forts when the heights are won, and the Army 
can correct the ships' fire. In each task they have to engage 
their targets, eitlier direct — that is, with the target visible — 
or indirect, when the target is concealed by intervening hills. 
Let us take the last case first. 
The sketches. Figures 1, 2, and 3, will make the neces- 
sary procedure clear. Figure 1 shows a ship. A, lying out 
at sea engaging a target, B, on shore, which is concealed from 
'A by an intervening hill, C. At F (to the left of C) is a 
higher hill in the possession of A's troops, from which A's 
fire is observed. E represents the coast line, and D is some 
conspicuous object — a rock or ruin on the coast, which is a 
convenient aiming point for the gunlayers in A. The general 
position of B in relation to A would have been ascertained 
by plans, maps, and charts; so that an approximate range 
can be put upon A's guns, and at the same time an approxi- 
mate deflection angle, DAB, put upon the sights, which 
then will be pointing at D, while the bore of the gun will be 
pointing towards B. The observers on the hUl F (or in aero- 
planes) will correct A's fire both for deflection and range; so 
that the angle, DAB, and the range, A B, wUI in a few 
rounds be ascertained with precision. 
7 
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y ^ 
D. /^"'^■^^^-^ 
\ 
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^^Juli^ 
A Ttfl.3. 
speed on a wavy course, coming in due time to A2 and then 
to A3, the range will have changed in aU from 15,000 yards 
to 15,500; but there will be many gradations up and down. 
Now, as A cannot keep the bearing of B, B being invisible, it 
v.ill be impossible to know the rate at which the range is 
changing, and consequently it will be impossible to keep an 
accurate range. But, further, the angle, DAB, wUl, of 
course, change monstrously. D therefore becomes valueless 
as an aiming point and the direction, as well as the range, 
of the target will become lost the moment A moves. 
Now, supposing that there were no hill at C, and B was 
visible from A wherever A proceeded to, then it would theo- 
retically be possible, by means of instruments built on the 
principle of Captain Dumaresq's, to have a constant indica- 
tion of the actual rate of change. But unless that rate is 
impressed upon the sight synchronously with its occurring, 
very serious errors int<3rven6, as would appear, for instance, 
from Figure 4. In Figure 4 the upper ship. A, is supposed 
to be descending from north to south towards the lower ship, 
B, which is proceeding from west to east. When at a range 
of 10,650 yards, A proceeds to make a 90 degrees turn, so as 
to come on a course parallel with B. This turn, we will sup- 
pose, takes one minute and a half to execute. In that minuta 
and a half the range will alter from 10,650 yards to 10,000 
yards. In the first half-minute the range is diminished by 
325 yards, in the second by 225 yards, in the third by 100 
yards. But the rate at the beginning of the first half-minuta 
is 375 yards per half -minute; at the beginning of the second 
half-minute is 300 per half-minute, and at the beginning cf 
the third is 175 yards per half -minute. If, then, these rates 
had been persisted in for the whole of each half-minute, there 
» ould have been an error of 50 yards in the first half -minute 
w 
^0 
I. 
Is: 
>2 
In \i[^ 50 seconds between I and 2 ttie rai^ehas clian^ed 52Si^ds 
»' • •^ • • O • * •• " ". • • * 100 • 
650 .. 
At I tiie rate of change was 3 TS^ds. per 30 seconds ""^^ 
It ^ m m • . ^ ' % WW W w •• ** M 
•frW» m ^ « %% L CO •% M,-A «• 
HocL these rates been appU£d, for 50 seconds 
contumous^. tfiere would baye been an error of 
SOi^ds inthe i^.^ 30 seconds 
If. . , 3^. » 
A Dotal of locT- — ^ "' 
Yi^.4 
12* 
