Page:Sim pall-mall-magazine 1904-01 32 129.pdf/26

20 but, on the other hand, as has been said, the dragging of the guide-rope's weight through the water, acted as a very effectual brake. As the speed of the air-ship is increased, this brake-like action of the guide-rope (like that of the resistance of the atmosphere itself) grows, not in proportion to the speed, but in proportion to the square of it.

Photo by Simons. On these flights along the Mediterranean coast the easy navigation afforded me by the maritime guide-rope was purchased, as nearly as I could calculate, by the sacrifice of about six kilometres per hour of speed ; but, with or without maritime guide-rope, the speed calculation has its own almost insurmountable difficulties.

From Monte Carlo to Cap Martin at ten o'clock of a given morning may be quite a different trip from Monte Carlo to Cap Martin at noon of the same day ; while from Cap Martin to Monte Carlo, except in perfect calm, must always be a still different proposition. Nor can any accurate calculations be based on the markings of the anemometer, an instrument which I nevertheless carried. Out of simple curiosity I made note of its readings on several occasions during my trip of February 12th, 1902. It seemed to be marking between 32 and 37 kilometres per hour ; but the wind, complicated by side-gusts, acting at the same time on the air-ship and the wings of the anemometer windmill—ie. on two moving systems whose inertia cannot possibly be compared—would alone be sufficient to falsify the result.

When, therefore, I state that, according to my best judgment, the average of my speed through the air on these flights was between 30 and 35 kilometres per hour, it will be understood that it refers to speed through the air whether the air be still or moving, and to speed retarded by the dragging of the maritime guide-rope. Putting this adverse influence at the moderate figure of 7 kilometres per hour, my speed through the still or moving air would be between 37 and 42 kilometres per hour.

Where speed calculations have their real importance is in affording necessary data for the construction of new and more powerful air-ships. Thus the balloon of my racing " No. 7," whose