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 19 interior pressure to withstand the exterior pressure of the atmosphere in front of the balloon as I drive against it.



Photo by Numa Blanc.

The speed problem is, doubtless, the first of all air-ship problems. Speed must always be the final test between rival air-ships ; and until high speed shall be arrived at, certain other problems of aerial navigation must remain in part unsolved. For example, take that of the air-ship's pitching (tangage). I think it quite likely that a critical point in speed will be found, beyond which on each side the pitching will be practically nil. When going slowly, or at moderate speed, I have experienced no pitching, which, in an air-ship like my " No. 6," seems always to commence at 25 to 30 kilometres per hour through the air. Now, probably, when one passes this speed considerably—say at the rate of 50 kilometres per hour—all tangage, or pitching, will be found to cease again.

Speed must always be the final test between rival air-ships, because in itself it sums up all other air-ship qualities, including "stability." At Monaco, when I made my best speed, however, I had no rivals to compete with. Furthermore, my prime study and amusement there was the beautiful working of the maritime guide-rope ; and this guide-rope, dragging through the water, must of necessity retard whatever speed I made. There could be no help for it. Such was the price I must pay for automatic equilibrium and vertical stability—in a word, easy navigation—so long as I remained the sole and solitary navigator of the air-ship.

Nor is it an easy task to calculate an air-ship's speed. On these flights up and down the Mediterranean coast, the speed of my return to Monaco, wonderfully aided by the wind, could bear no relation to the speed out, retarded by the wind ; and there was nothing to show that the force of the wind, going and coming, was constant. It is true that on these flights one of the difficulties standing in the way of such speed calculations the "shoot the chutes" (mentagnes Russes) of ever-varying—altitude was done away with by the operation of the marine guide-rope ;