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tion. In fact, the art of managing a true flying machine is so refined and the skill required so great, and in the absence of such skill the danger of a first attempt is so extreme, that probably the only way to achieve true flight would be by the use first of a dirigible balloon, and then gradually to decrease the sustaining gas and substitute the aëroplane and propeller.

In the distant future, and by means of such gradual approaches, the engineering difficulties in the way of a true flying machine may be finally overcome. If so, then we may look for the greatest success in the direction of the work of Langley and Maxim.

Addendum, January 23, 1894.

The above article was finished and sent to the publisher some time in October, 1893. In the January number of the American Journal of Science Prof. Langley published an account of another epoch-making series of experiments bearing on this subject. In his previous series he showed the enormous importance of onward movement in the sustaining power of an aëroplane. In this he shows the enormous variation of velocity in air currents from moment to moment. The whole air is in a violent turmoil from varying currents. In the above article I have shown that soaring and sailing are impossible without differential air currents; but the amount of difference of velocity of these currents shown by Prof. Langley was wholly unexpected. These experiments, therefore, show that the supply of force from this source available to the bird or to the flying machine is far greater than previously supposed. While they do not seriously vitiate any of my conclusions, they certainly place the subject of artificial flight in a still more hopeful light.


Mr. Bruce, of the Dundee antarctic whaling fleet, describes the whole of the district south of 60° south latitude as strewn with icebergs, which become very numerous south of 62°. On one day the author counted at one time from deck sixty-five of great size, besides many smaller ones. The highest berg seen from his vessel, the Balaena, was about two hundred and fifty feet high; but many were not more than seventy or eighty feet, the average possibly being about one hundred and fifty feet high. All these bergs are tabular, or weather-worn varieties of the tabular forms. They become pierced with caves, and these are sometimes connected with funnel holes, through which, as the swell beats up the caves, immense columns of spray are projected. They may be finely castellated, pillared, or arched. One was beautifully conical. The base of the bergs was colored pale brown by marine organisms, and other brown streaks were seen beyond the water-level. No luminous glow was observed. "Clothed in mist, they raise their mighty snow-clad shoulders to a stately height, or shine forth brilliantly in the sun. Although they are of the purest white, yet they glow with color. The crevices exhibit rich cobaltic blue, and everywhere are splashes of emerald green."