Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . e distance of the point ofdescent, it is easy to fix the level at which the valve must beopened. The rate of falling is about 6 miles an hour, and letus suppose that the balloon is travelling at a speed of 12 milesan hour, the distance of the spot selected for landing being onemile, , 5,280 ft. The height at which the valve must beopened will be -fy X 5,280, , 2,640 ft. Shortly before thelanding place is reached the balloon must be brought to res
Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . e distance of the point ofdescent, it is easy to fix the level at which the valve must beopened. The rate of falling is about 6 miles an hour, and letus suppose that the balloon is travelling at a speed of 12 milesan hour, the distance of the spot selected for landing being onemile, , 5,280 ft. The height at which the valve must beopened will be -fy X 5,280, , 2,640 ft. Shortly before thelanding place is reached the balloon must be brought to rest bymeans of the guide-rope, ballast being thrown out if necessary. 1 See Dr. Richard Emdens article on the Theory of Landing,* in the IllnstrierteAeronaiitiscJie Mitteilungen for March, 1906. 232 AIRSHIPS PAST AND PRESENT. This is a very simple matter if there are no telegraph wires orother obstacles. But this seldom happens; there are usuallytrees or something of the kind in the way, and then it is neces-sary to proceed cautiously, for fear of getting entangled. Ballastmust be thrown out in order to avoid these obstacles and rise ?. Fig. 143.—Dillingen, seen through the clouds.(Photograph by A. Riedinger, of Augsburg.) above them; but care must be taken that the balloon does notrise too much, otherwise there is a danger of its rising to theheight from which it has fallen. After leaping over the obstacle,the valve must be pulled at once and the balloon brought to theground. Such manoeuvres can be very tedious ; sometimes it isnecessary to jump over houses and villages, which must on noaccount be touched by the guide-rope if there is still sufficient BALLOONING AS A SPOKT. 233 ballast to be able to rise above them. The importance of reservinga certain amount of ballast for the end of the journey will nowbe evident. A journey cannot be continued till all the ballast isthrown away, leaving none for the purpose of landing; other-wise a guide-rope, rattling along the tops of hous
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