It is a well-known fact that certain soaring birds cannot leave the ground when once they have alighted, except by an initial run to acquire the necessary speed; and every goose hunter is familiar with the manner in which these birds run along the surface of water, flapping their wings and skimming along some distance before they acquire sufficient velocity to mount into the air. A description of a similar action of an eagle in leaving the earth, written by a careful observer a few years ago, has become classic. This huntsman had come upon an eagle which had alighted upon the sandy banks of the Nile, and had fired at it, thus stimulating the bird to its utmost energy in getting into flight. Yet on examining the foot-marks made in the sand it was found that, even under these circumstances, the bird had been obliged to run "full twenty yards before he could raise himself from the earth. The marks of his claws were traceable on the sandy soil," says the writer, "as, at first with firm and decided digs, he found his way, but as he lightened his body and increased his speed with the aid of his wings, the imprints of his talons gradually merged into long scratches." It is evident that if such a master of the art of flying as an eagle must thus acquire initial velocity before flight is possible, a human novice must do considerably more. The method that would naturally suggest itself would be that of running down the slope of a hillside, and Lilienthal adopted this method, beginning his flights by running down the gentle slope of a hill against the wind, until the requisite momentum was acquired. This was, indeed, a reversion to some of the oldest types of flying-machines, but with this difference--that it was the result of scientific study. The results attained proved that the theory was not visionary--that scientists had not dreamed and studied in vain. For, as little by little the experimenter gained experience, he was able to soar farther and farther in his birdlike machine, in one flight sailing a distance of twelve hundred feet. Under certain favorable wind conditions he could sail from a hilltop without the initial run, and at times he actually rose in the air to a point higher than that from which he started.