the Society, which was held at the Society of Arts under the
Presidency of the Duke of Argyll, was the means of bringing
Stringfellow back into the field. It was Wenham's suggestion,
in the first place, that monoplane design should be abandoned
for the superposition of planes; acting on this suggestion
Stringfellow constructed a model triplane, and also designed a
steam engine of slightly over one horse-power, and a one
horse-power copper boiler and fire box which, although capable
of sustaining a pressure of 500 lbs. to the square inch, weighed
only about 40 lbs.

Both the engine and the triplane model were exhibited at the
first Aeronautical Exhibition held at the Crystal Palace in
1868. The triplane had a supporting surface of 28 sq. ft.;
inclusive of engine, boiler, fuel, and water its total weight
was under 12 lbs. The engine worked two 21 in. propellers at
600 revolutions per minute, and developed 100 lbs. steam
pressure in five minutes, yielding one-third horse-power. Since
no free flight was allowed in the Exhibition, owing to danger
from fire, the triplane was suspended from a wire in the nave of
the building, and it was noted that, when running along the
wire, the model made a perceptible lift.

A prize of L100 was awarded to the steam engine as the lightest
steam engine in proportion to its power. The engine and model
together may be reckoned as Stringfellow's best achievement. He
used his L100 in preparation for further experiments, but he
was now an old man, and his work was practically done. Both the
triplane and the engine were eventually bought for the
Washington Museum; Stringfellow's earlier models, together with