<h2><SPAN name="CHAPTER_IX" id="CHAPTER_IX">CHAPTER IX</SPAN><br/> <span class="subhead"><span class="smcap">Getting the Range</span></span></h2>
<p class="drop-cap4"><span class="smcap1">Every</span> person with a good pair of eyes in
his head is a range-finder. He may not
know it, but he is, just the same, and the way to
prove it is to try a little range-finding on a small
scale.</p>
<p>Use the top of a table for your field of operations,
and pick out some spot within easy reach
of your hand for the target whose range you
wish to find. The target may be a penny or a
small circle drawn on a piece of white paper.
Take a pencil in your hand and imagine it is
a shell which you are going to land on the
target. It is not quite fair to have a bird's-eye
view of the field, so get down on your knees and
bring your eyes within a few inches of the top
of the table. Now close one eye and making
your hand describe an arc through the air, like
the arc that a shell would describe, see how
nearly you can bring the pencil-point down on<span class="pagenum"><SPAN name="Page_170" id="Page_170">170</SPAN></span>
the center of the target. Do it slowly, so that
your eye may guide the hand throughout its
course. You will be surprised to find out how
far you come short, or overreach the mark.
You will have actually to grope for the target.
If by any chance you should score a hit on the
first try, you may be sure that it is an accident.</p>
<p>Have a friend move the target around to a
different position, and try again. Evidently,
with one eye you are not a good range-finder;
but now use two eyes and you will score a hit
every time. Not only can you land the pencil
on the penny, but you will be able to bring it
down on the very center of the target.</p>
<p>The explanation of this is that when you
bring your eyes to bear upon any object that
is near by, they have to be turned in slightly, so
that both of them shall be aimed directly at
that object. The nearer the object, the more
they are turned in, and the farther the object,
the more nearly parallel are the eyes. Long
experience has taught you to gage the distance
of an object by the feel of the eyes—that is, by
the effort your muscles have to make to pull
the eyes to a focus—and in this way the eyes
give you the range of an object. You do not<span class="pagenum"><SPAN name="Page_171" id="Page_171">171</SPAN></span>
know what the distance is in feet or inches, but
you can tell when the pencil-point has moved
out until it is at the same focus as the target.</p>
<p>The experiment can be tried on a larger scale
with the end of a fishing-rod, but here you will
probably have to use a larger target. However,
there is a limit to which you can gage the range.
At a distance of, say, fifteen or twenty feet, a
variation of a few inches beyond or this side
of the target makes scarcely any change in the
focus of the eyes. That is because the eyes are
so close together. If they were farther apart,
they could tell the range at much greater distances.</p>
<h3>SPREADING THE EYES FAR APART</h3>
<p>Now the ordinary range-finder, used in the
army and in the navy, is an arrangement for
spreading the eyes apart to a considerable distance.
Of course the eyes are not actually
spread, but their vision is. The range-finder is
really a double telescope. The barrel is not
pointed at an object, but it is held at right angles
to it. You look into the instrument at the middle
of the barrel and out of it at the two ends.
A system of mirrors or prisms makes this possible.<span class="pagenum"><SPAN name="Page_172" id="Page_172">172</SPAN></span>
The range-finder may be a yard or more
in length, which is equivalent to spreading your
eyes a yard or more apart. Now, the prisms or
object-glasses at the ends of the tube are adjustable,
so that they will turn in until they
focus directly on the target whose range you
wish to find, and the angle through which these
glasses are turned gives a measure of the distance
of the target. The whole thing is calculated
out so that the distance in feet, yards,
or meters, or whatever the measure may be, is
registered on a scale in the range-finder. Ordinarily
only one eye is used to look through the
range-finder, because the system of mirrors is
set to divide the sight of that one eye and make
it serve the purposes of two. That leaves the
other eye free to read the scale, which comes
automatically into view as the range-finder is
adjusted for the different ranges.</p>
<p>On the battle-ships enormous range-finders
are used. Some of them are twenty feet long.
With the eyes spread as far apart as that and
with a microscope to read the scale, you can
imagine how accurately the range can be found,
even when the target is miles away. But on
land such big range-finders cannot conveniently<span class="pagenum"><SPAN name="Page_173" id="Page_173">173</SPAN></span>
be used; they are too bulky. When it is necessary
to get the range of a very distant object,
two observers are used who are stationed several
hundred yards apart. These observers
have telescopes which they bear upon the object,
and the angle through which they have to
turn the telescope is reported by telephone to
the battery, where, by a rapid calculation, it is
possible to estimate the exact position of the
target. Then the gun is moved up or down, to
the right or to the left, according to the calculation.
The observers have to creep as near
to the enemy as possible and they must be up
high enough to command a good view of the
target. Sometimes they are placed on top of
telegraph poles or hidden up a tall tree, or in
a church steeple.</p>
<h3>GETTING THE OBSERVER OFF THE GROUND</h3>
<p>This was the method of getting the range in
previous wars and it was used to a considerable
extent in the war we have just been through.
But the great European conflict brought out
wonderful improvements in all branches of
fighting; and range-finding was absolutely revolutionized,
because shelling was done at greater<span class="pagenum"><SPAN name="Page_174" id="Page_174">174</SPAN></span>
ranges than ever before, but chiefly because the
war was carried up into the sky.</p>
<p>A bird's-eye observation is much more accurate
than any that can be obtained from the
ground. Even before this war, some observations
were taken by sending a man up in a kite,
particularly a kite towed from a ship, and even
as far back as the Civil War captive balloons
were used to raise an observer to a good height
above the ground. They were the ordinary
round balloons, but the observation balloon of
to-day is a very different-looking object. It is
a sausage-shaped gas-bag that is held on a slant
to the wind like a kite, so that the wind helps
to hold it up. To keep it head-on to the wind,
there is a big air-bag that curls around the
lower end of the sausage. This acts like a rudder,
and steadies the balloon. Some balloons
have a tail consisting of a series of cone-shaped
cups strung on a cable. A kite balloon will ride
steadily in a wind that would dash a common
round balloon in all directions. Observers in
these kite balloons are provided with telephone
instruments by which they can communicate instantly
with the battery whose fire they are directing.
But a kite balloon is a helpless object;<span class="pagenum"><SPAN name="Page_175" id="Page_175">175</SPAN></span>
it cannot fight the enemy. The hydrogen gas
that holds it up will burn furiously if set on
fire. In the war an enemy airplane had merely
to drop a bomb upon it or fire an incendiary bullet
into it, and the balloon would go up in smoke.
Nothing could save it, once it took fire, and all
the observers could do was to jump for their
lives as soon as they saw the enemy close by.
They always had parachutes strapped to them,
so they could leap without an instant's delay in
case of sudden danger. At the very first approach
of an enemy airplane, the kite balloon
had to be hauled down or it would surely be destroyed,
and so kite balloons were not very dependable
observation stations for the side
which did not control the air.</p>
<p>As stated in the preceding chapter, just before
the fighting came to an end, our army was
preparing to use balloons that were not afraid
of flaming bullets, because they were to be filled
with a gas that would not burn.</p>
<h3>MAKING MAPS WITH A CAMERA</h3>
<p>Because airplanes filled the sky with eyes,
everything that the army did near the front
had to be carefully hidden from the winged<span class="pagenum"><SPAN name="Page_176" id="Page_176">176</SPAN></span>
scouts. Batteries were concealed in the woods,
or under canopies where the woods were shot
to pieces, or they were placed in dugouts so that
they could not be located. Such targets could
seldom be found with a kite balloon. It was
the task of airplane observers to search out
these hidden batteries. The eye alone was not
depended upon to find them. Large cameras
were used with telescopic lenses which would
bring the surface of the earth near while the
airplane flew at a safe height. These were
often motion-picture cameras which would automatically
make an exposure every second, or
every few seconds.</p>
<div id="ip_176" class="figcenter" style="width: 545px;">
<ANTIMG src="images/i_176.jpg" width-obs="545" height-obs="353" alt="" /><br/>
<div class="captionl">(C) Underwood & Underwood</div>
<div class="caption0">British Anti-aircraft Section getting the Range of an Enemy Aviator</div>
</div>
<p>When the machine returned from a photographing-expedition,
the films were developed
and printed, and then pieced together to form a
photographic map. The map was scrutinized
very carefully for any evidence of a hidden battery
or for any suspicious enemy object. As
the enemy was always careful to disguise its
work, the camera had to be fitted with color-screens
which would enable it to pick out details
that would not be evident to the eye. As
new photographic maps were made from day to
day, they were carefully compared one with<span class="pagenum"><SPAN name="Page_177" id="Page_177">177</SPAN></span>
the other so that it might be seen if there was the
slightest change in them which would indicate
some enemy activity. As soon as a suspicious
spot was discovered, its position was noted on
a large-scale military map and the guns were
trained upon it.</p>
<div id="ip_177" class="figcenter" style="width: 540px;">
<ANTIMG src="images/i_177.jpg" width-obs="540" height-obs="350" alt="" /><br/>
<div class="captionl">(C) Kadel & Herbert</div>
<div class="caption0">A British Aviator making Observations over the German Lines</div>
</div>
<h3>CORRECTING THE AIM</h3>
<p>It is one thing to know where the target is and
another to get the shell to drop upon it. In the
firing of a shell a distance of ten or twenty miles,
the slightest variation in the gun will make a
difference of many yards in the point where the
shell lands. Not only that, but the direction of
the wind and the density of the air have a part
to play in the journey of the shell. If the shell
traveled through a vacuum, it would be a much
simpler matter to score a hit by the map alone.
But even then there would be some differences,
because a gun has to be "warmed up" before it
will fire according to calculation. That is why
it is necessary to have observers, or "spotters"
as they are called, to see where the shell actually
do land and tell the gun-pointers whether
to elevate or depress the gun, and how much to
"traverse" it—that is, move it sideways. This<span class="pagenum"><SPAN name="Page_178" id="Page_178">178</SPAN></span>
would not be a very difficult matter if there
were only one gun firing, but when a large number
of guns are being used, as was almost invariably
the case in the war, the spotter had to
know which shell belonged to the gun he was
directing.</p>
<p>One of the most important inventions of the
war was the wireless telephone, which airplanes
used and which were brought to such perfection
that the pilot of an airplane could talk to a
station on the earth without any difficulty,
from a distance of ten miles; and in some
cases he could reach a range of fifty miles.
With the wireless telephone, the observer could
communicate instantly with the gun-pointer,
and tell him when to fire. Usually thirty seconds
were allowed after the signal sent by the
observer before the gun was fired, and on the instant
of firing, a signal was sent to the man in
the airplane to be on the lookout for the shell.
Knowing the position of the target, the gun-pointer
would know how long it would take the
shell to travel through the air, and he would
keep the man in the airplane posted, warning
him at ten seconds, five seconds, and so forth,
before the shell was due to land.</p>
<p><span class="pagenum"><SPAN name="Page_179" id="Page_179">179</SPAN></span>
In order to keep the eyes fresh for observation
and not to have them distracted by other sights,
the observer usually gazed into space until just
before the instant the shell was to land. Then
he would look for the column of smoke produced
by the explosion of the shell and report
back to the battery how far wide of the mark
the shell had landed. A number of shell would
be fired at regular intervals, say four or five per
minute, so that the observer would know which
shell belonged to the gun in question.</p>
<p>There are different kinds of shell. Some
will explode on the instant of contact with the
earth. These are meant to spread destruction
over the surface. There are other shell which
will explode a little more slowly and these penetrate
the ground to some extent before going off;
while a third type has a delayed action and is
intended to be buried deep in the ground before
exploding, so as to destroy dugouts and underground
positions. The bursts of smoke from
the delayed-action shell and the semi-delayed-action
shell rise in a slender vertical column and
are not so easily seen from the sky. The instantaneous
shell, however, produces a broad burst
of smoke which can be spotted much more<span class="pagenum"><SPAN name="Page_180" id="Page_180">180</SPAN></span>
readily, and this enables the man in the airplane
to determine the position of the shell with
greater accuracy. For this reason, instantaneous
shell were usually used for spotting-purposes,
and after the gun had found its target,
other shell were used suited to the character of
the work that was to be done.</p>
<h3>MINIATURE BATTLE-FIELDS</h3>
<p>Observation of shell-fire from an airplane
called for a great deal of experience, and our
spotters were given training on a miniature
scale before they undertook to do spotting from
the air. A scaffolding was erected in the training-quarters
over a large picture of a typical bit
of enemy territory. Men were posted at the
top of this scaffolding so that they could get a
bird's-eye view of the territory represented on
the map, and they were connected by telephone
or telegraph with men below who represented
the batteries. The instructor would flash a little
electric light here and there on the miniature
battle-field, and the observers had to locate these
flashes and tell instantly how far they were
from certain targets. This taught them to be
keen and quick and to judge distance accurately.<span class="pagenum"><SPAN name="Page_181" id="Page_181">181</SPAN></span>
Airplane observing was difficult and dangerous,
and often impossible. On cloudy days the observer
might be unable to fly at a safe height
without being lost in the clouds. Then dependence
had to be placed upon observers stationed
at vantage-points near the enemy, or in kite
balloons.</p>
<h3>SPOTTING BY SOUND</h3>
<p>When there is no way of seeing the work of
a gun, it is still possible to correct the aim, because
the shell can be made to do its own spotting.
Every time a shell lands, it immediately
announces the fact with a loud report. That
report is really a message which the shell sends
out in all directions with a speed of nearly 800
miles per hour—1,142 feet per second, to be
exact. This sound-message is picked up by a
recorder at several different receiving-stations.
Of course it reaches the nearest station a fraction
of a second before it arrives at the next
nearest one. The distance of each station from
the target is known by careful measurement on
the map, and the time it takes for sound to
travel from the target to each station is accurately
worked out. If the sound arrives at each<span class="pagenum"><SPAN name="Page_182" id="Page_182">182</SPAN></span>
station on schedule time, the shell has scored a
hit; but if it reaches one station a trifle ahead
of time and lags behind at another, that is evidence
that the shell has missed the target and a
careful measure of the distance in time shows
how far and in what direction it is wide of the
mark. In this way it was possible to come
within fifty or even twenty-five yards of the
target.</p>
<p>This sound-method was also used to locate
an enemy battery. It was often well nigh impossible
to locate a battery in any other way.
With the use of smokeless powder, there is
nothing to betray the position of the gun, except
the flash at the instant of discharge, and
even the flash was hidden by screens from the
view of an airplane. Aside from this, when an
airplane came near enough actually to see one
of these guns, the gun would stop firing until the
airplane had been driven off. But a big gun
has a big voice, and it is impossible to silence
it. Often a gun whose position has remained
a secret for a long time was discovered because
the gun itself "peached."</p>
<p>The main trouble with sound-spotting was
that there were usually so many shell and guns<span class="pagenum"><SPAN name="Page_183" id="Page_183">183</SPAN></span>
going off at the same time that it was difficult
if not impossible to distinguish one from another.
Sometimes the voice of a hidden gun
was purposely drowned by the noise of a lot of
other guns. After all, the main responsibility
for good shooting had to fall on observers who
could actually see the target, and when we think
of the splendid work of our soldiers in the war,
we must not forget to give full credit to the
tireless men whose duty it was to watch, to
the men on wings who dared the fierce battle-planes
of the enemy, to the men afloat high in
the sky who must leap at a moment's notice
from under a blazing mass of hydrogen, and
finally to the men who crept out to perilous
vantage-points at risk of instant death, in order
to make the fire of their batteries tell.</p>
<hr />
<p><span class="pagenum"><SPAN name="Page_184" id="Page_184">184</SPAN></span></p>
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