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observes whether the shell has burst to the right or to the left
of the objective and corrects accordingly。 The observer commands
C to fire； and another shell is launched which emits a yellow
flame and smoke。 It bursts at 2 according to the observer； while
gunner C also notes whether it is to the right or to the left of
the target and corrects accordingly。 Now gunner D receives the
command to fire and the shell which explodes at 3 throws off a
white flame and smoke。 Gunner D likewise observes whether there
is any deviation to right or left of the target and corrects in a
similar manner。 From the sum of the three rounds the observer
corrects the altitude； completes his calculations； and
communicates his instructions for correction to the three
gunners； who now merely train their weapons for altitude。 The
objective is to induce the shells hurled from the three corners
of the triangle to burst at a common point 4； which is considered
to be the most critical spot for the aviator。 The fire is then
practically concentrated from the three weapons upon the apex of
a triangular cone which is held to bring the machine within the
danger zone。
This method of finding the range is carried out quicklytwo or
three seconds being occupied in the task。 In the early days of
the war the German anti…aircraft artillerymen proved sadly
deficient in this work； but practice improved their fire to a
marvellous degree； with the result that at the moment it is
dangerous for an aviator to essay his task within an altitude of
6；000 feet； which is the range of the average anti…aircraft gun。
The country occupied by a belligerent is divided up in this
manner into a series of triangles。 For instance； a machine
entering hostile territory from the east； enters the triangle
A…B…C； and consequently comes within the range of the guns posted
at the comers of the triangle。 Directly he crosses the line B…C
and enters the adjacent triangle he passes beyond the range of
gun A but comes within the range of the gun posted at D； and
while within the triangular area is under fire from the guns
B…C…D。 He turns and crosses the line A…C； but in so doing enters
another triangle A…C…E； and comes range of the gun posted at E。
The accompanying diagram represents an area of country divided up
into such triangle and the position of the guns； while the circle
round the latter indicate the training arc of the weapons； each
of which is a complete circle； in the horizontal plane。 The
dotted line represents the aviator's line of flight； and it will
be seen that no matter how he twists and turns he is always
within the danger zone while flying over hostile territory。 The
moment he outdistances one gun he comes within range of another。
The safety of the aviator under these circumstances depends upon
his maintaining an altitude exceeding the range of the guns
below； the most powerful of which have a range of 8；000 to 10；000
feet； or on speed combined with rapid twisting and turning； or
erratic undulating flight； rendering it extremely difficult for
the gun…layer to follow his path with sufficient celerity to
ensure accurate firing。
At altitudes ranging between 4；000 and 6；000 feet the aeroplane
comes within the range of rifle and machine…gun firing。 The
former； however； unless discharged in volleys with the shots
covering a wide area； is not particularly dangerous； inasmuch as
the odds are overwhelmingly against the rifleman。 He is not
accustomed to following and firing upon a rapidly moving
objective； the result being that ninety…nine times out of a
hundred he fails to register a hit。 On the other hand the
advantage accruing from machine…gun fire is； that owing to the
continuous stream of bullets projected； there is a greater
possibility of the gun being trained upon the objective and
putting it hors de combat。
But； taking all things into consideration； and notwithstanding
the achievements of the artillerist； the advantages are
overwhelmingly on the side of the aviator。 When one reflects
upon the total sum of aircraft which have been brought to earth
during the present campaign； it will be realised that the number
of prizes is insignificant in comparison with the quantity of
ammunition expended。
CHAPTER XVI
MINING THE AIR
While the anti…aircraft gun represents the only force which has
been brought to the practical stage for repelling aerial attack；
and incidentally is the sole offensive weapon which has
established its effectiveness； many other schemes have been
devised and suggested to consummate these ends。 While some of
these schemes are wildly fantastic； others are feasible within
certain limitations； as for instance when directed against
dirigibles。
It has been argued that the atmosphere is akin to the salt seas；
that an aerial vessel in its particular element is confronted
with dangers identical with those prevailing among the waters of
the earth。 But such an analogy is fallacious： there is no more
similarity between the air and the ocean than there is between an
airship and a man…of…war。 The waters of the earth conceal from
sight innumerable obstructions； such as rocks； shoals； sandbanks；
and other dangers which cannot by any means be readily detected。
But no such impediments are encountered in the ether。 The craft
of the air is virtually a free age in the three dimensions。 It
can go whither it will without let or hindrance so long as the
mechanical agencies of man are able to cope with the influences
of Nature。 It can ascend to a height which is out of all
proportion to the depth to which the submarine can descend in
safety。 It is a matter of current knowledge that a submarine
cannot sink to a depth of more than 250 feet： an aerial vessel is
able to ascend to 5；000； 8；000； or even 10；000 feet above the
earth； and the higher the altitude it attains the greater is its
degree of safety。 The limit of ascension is governed merely by
the physical capacities of those who are responsible for the
aerial vessel's movement。
It is for this reason that the defensive measures which are
practised in the waters of the earth are inapplicable to the
atmosphere。 Movement by； or in； water is governed by the depth
of channels； and these may be rendered impassable or dangerous to
negotiate by the planting of mines。 A passing ship or submarine
may circumvent these explosive obstructions； but such a
successful manoeuvre is generally a matter of good luck。 So far
as submarines are concerned the fact must not be over looked that
movements in the sea are carried out under blind conditions： the
navigator is unable to see where he is going； the optic faculty
is rendered nugatory。 Contrast the disability of the submarine
with the privileges of its consort in the air。 The latter is
able to profit from vision。 The aerial navigator is able to see
every inch of his way； at least during daylight。 When