touch with the
other arms. Photographic cameras and fittings were still very imperfect,
and photography from the air was not much practised, but sketch-maps of
enemy trenches and gun-pits, as located by air reconnaissances, were
issued by Headquarters during the battle of Ypres. Good work was done in
directing the fire of the artillery, and the few wireless machines were
much in demand. A telegram sent on the 28th of October from Sir Horace
Smith-Dorrien to the Royal Flying Corps headquarters runs: 'Can you send
us a second machine, with wireless installation, for use to-morrow? The
aeroplane now working without wireless with Fifth Division has more to
do than it can accomplish owing to observation being required for French
artillery as well as our own.' But the wireless machine was required by
the First Corps, at the northern end of the line, and a machine without
wireless was sent instead.

The deadly and effective method of directing artillery fire on hostile
batteries by means of wireless telegraphy played a great part in winning
the war, but for the first battle of Ypres the wireless machines were
not ready in quantity. The penalty which had to be paid for this
unreadiness was heavy. Precious shells, which were all too few, had to
be expended for ranging purposes. On the 4th of November Lord Kitchener
wired to Sir John French: 'I have been talking to David Henderson about
giving more observation to artillery by aeroplanes. As this saves the
ranging ammunition, which is worth anything to us, please insist upon
it.' Failing wireless, other methods of ranging had to be employed.
These methods had been set forth in an official paper issued on the 28th
of October. The aeroplane flies at any convenient height and when it is
exactly above the target it fires a Very light. The battery
range-finders, who have been following its course, then take its range
and another observer with the battery takes its angle of elevation.
These two observations are sufficient to determine the horizontal
distance between the battery and the target. It was sometimes found
difficult to take the range of an aeroplane, at a given moment, with an
ordinary range-finder, and an alternative method of ranging is
suggested. By this method the aeroplane flies at a prearranged height,
and, as before, fires a light exactly over the target. But this method
also is liable to error, for an aeroplane determines its height by the
use of a barometer, and baro