Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . ding to thepoint of view. Stillhe made no exactmeasurements ofthe force of thewind, and con-tented himself withestimates. Conse-quently his state-ments under thishead must bereceived withcaution. On theother hand, it isonly fair to allowthat the instru-ments at presentin use for themeasurement ofthe wind are not altogether satisfactory. Perhaps the best ofthem is the one made by Gradenwitz. It depends on the gyro-static principle involved in the construc
Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . ding to thepoint of view. Stillhe made no exactmeasurements ofthe force of thewind, and con-tented himself withestimates. Conse-quently his state-ments under thishead must bereceived withcaution. On theother hand, it isonly fair to allowthat the instru-ments at presentin use for themeasurement ofthe wind are not altogether satisfactory. Perhaps the best ofthem is the one made by Gradenwitz. It depends on the gyro-static principle involved in the construction of instruments fordetermining the velocities of fluids. If a glass cylinder is filledwith fluid, and rotated about a vertical axis, the upper surface ofthe fluid assumes the shape of a paraboloid of revolution, and thedepression depends, as far as its magnitude is concerned, on thespeed of rotation. If such an instrument is calibrated experi-mentally it is possible to determine the speed of rotation by notingthe extent of the depression, always assuming that the volume ofthe fluid remains unchanged. Gradenwitzs instrument consists. Fig. 37.—Gradenwitz anemometer. 70 AIRSHIPS PAST AND PRESENT. in the combination of a Robinson anemometer with a closedglass tube containing the fluid. The apparatus is set inmotion by the wind, in the usual way, and it is then possible bynoting the depression to tell the velocity at any instant. Thecalibration is carried out by means of the rotating apparatusused by the Meteorological Observatory at Hamburg. Aninstrument of this sort ought always to be used in trials ofdirigible balloons. But even without taking into account anysuch measurements, the power given by the motor in Dumontslast balloon was much too small. He therefore changed it forone having four cylinders; it weighed much more, and it wastherefore necessary to add to the size of the balloon by insertinga piece in the middle. At the same time he set to work on themaking of a keel
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Keywords: ., bookcentury1900, bookdecade1900, bookpubl, booksubjectaeronautics
