twin pumps, double jet carburetors, and are usually
operated on mixtures consisting of one part benzol with one part
alcohol.

CHAPTER LIV

AEROPLANE IMPROVEMENTS--GIANT MACHINES--TECHNICAL DEVELOPMENTS

The experience gathered in the first eighteen months of the war by the
aviators of the hostile armies has done more for the development of
aeroplanes than many years of peaceful improvements could possibly
have accomplished. The ever increasing size, power and stability of
the heavier-than-air machine is plainly shown in the latest types of
battle planes, in which a spread of wings exceeding seventy-five feet
is no longer a novelty. True, the heralded approach of the gigantic
German battle triplanes did not take place in the second year of the
Great War, although it is an incontrovertible fact that such machines
have been built and are being used for some purpose. But none of them
took part in the fighting on the western front, nor has one of them
been seen on the Russian battle lines. There is reason to believe,
however, that these planes are used in naval reconnoitering, and their
great size permits of the carrying of large supplies of fuel, giving
them a great cruising radius. Reports from steamers plying the Baltic
state that gigantic aeroplanes have been sighted high up in the air by
captains and officers on Swedish and Danish ships, seemingly
maintaining a careful patrol of that sea against possible Russian and
British naval exploits.

There have been numerous unconfirmed reports concerning the use of
_cellon_, a tough and yet completely transparent material, in the
construction of aeroplanes on the German side, and occasional hints of
new "invisible" machines were dropped now and then. The reports
probably are based on some foundation of fact, but there is little to
show that _cellon_ is used to any large extent by the Teuton forces.
Samples of the material reached New York late in 1915, but the actual
uses to which it was put were not known at the time.

The tendency in recent months, especially on the western battle front,
has been the "attack in squadrons," instead of the individual combats
which made international heroes out of Boillot, Immelmann, Boelke,
Warneford and Navarre. The squadron attack was first employed by the
Germans in the Verdun operations. Previous to that time, only bombing
expeditions had been undertaken en masse, as many as sixty aeroplanes
taking part in a single attack. Bu