would propel and sustain in horizontal flight at a velocity of about forty miles an hour a little over 200 pounds. Langley's experiments were in the main made with a whirling-table which forces the model to move in horizontal flight and at a fixed angle. In 1887, however, he began experiments with free-flying models at the Allegheny Observatory, following Pinaud in using twisted rubber as motive power. Some forty models were made, but while, as Pinaud had shown, a small toy could be made to fly for a few seconds, the motive power was inadequate for a larger machine or a longer flight.
In 1891 Langley began the construction of a steam engine. Daimler had invented the internal-combustion engine in 1885, but its possibilities were not at first realized, and it was necessary to wait for the development of the automobile to demonstrate the remarkable combination of power and lightness in an engine which has made possible the contemporary aeroplane. After innumerable experiments a steam engine was constructed weighing about six pounds and of approximately one horse power. An aerodrome, chiefly of steel, weighing, apart from fuel and water, about twenty-four pounds, was launched on the Potomac River on May 6, 1896, and flew for over half a mile. It alighted with safety and performed a second flight on the same day. This was a performance of great historic interest. The paths of the aerodrome on May 6 and again on November 28 are here reproduced, as also an instantaneous photograph of the aerodrome in the air, which bears a remarkable resemblance to a contemporary picture.
In 1898 the board of ordnance and fortifications of the war department appropriated $50,000 for experiments with a man-carrying aerodrome. Langley was at first indisposed to complete the work which he had carried so far, believing that might be left to commercial enterprise. It was, however, undertaken with the assistance of Mr. Manly, who now describes the results in this memoir. The great difficulty, as before, was with the engine. A New York builder could not supply the