ciple of the apparatus, which was to obtain large supporting
surfaces without increasing unduly the leverage and consequent weight of
spar required, by simply superposing the surfaces.

This principle is entirely sound and it is surprising that it is,
to this day, not realized by those aviators who are hankering for
monoplanes.

Experiments by Stringfellow.

The next man to test an apparatus with superposed surfaces was Mr.
Stringfellow, who, becoming much impressed with Mr. Wenham's proposal,
produced a largish model at the exhibition of the Aeronautical Society
in 1868. It consisted of three superposed surfaces aggregating 28 square
feet and a tail of 8 square feet more. The weight was under 12 pounds
and it was driven by a central propeller actuated by a steam engine
overestimated at one-third of a horsepower. It ran suspended to a wire
on its trials but failed of free flight, in consequence of defective
equilibrium. This apparatus has since been rebuilt and is now in the
National Museum of the Smithsonian Institution at Washington. Linfield's
Unsuccessful Efforts.

In 1878 Mr. Linfield tested an apparatus in England consisting of a
cigar-shaped car, to which was attached on each side frames five feet
square, containing each twenty-five superposed planes of stretched and
varnished linen eighteen inches wide, and only two inches apart, thus
reminding one of a Spanish donkey with panniers. The whole weighed two
hundred and forty pounds. This was tested by being mounted on a flat car
behind a locomotive going 40 miles an hour. When towed by a line fifteen
feet long the apparatus rose only a little from the car and exhibited
such unstable equilibrium that the experiment was not renewed. The lift
was only about one-third of what it would have been had the planes been
properly spaced, say their full width apart, instead of one-ninth as
erroneously devised.

Renard's "Dirigible Parachute."

In 1889 Commandant Renard, the eminent superintendent of the French
Aeronautical Department, exhibited at the Paris Exposition of that year,
an apparatus experimented with some years before, which he termed a
"dirigible parachute." It consisted of an oviform body to which were
pivoted two upright slats carrying above the body nine long superposed
flat blades spaced about one-third of their width apart. When this
apparatus was properly set at an angle to the longitudinal axis of the
body and dropped from a balloon, it travelled bac