the slip or dive, had come to earth. But these falls did not hurt him, nor did they damage his machine; so he was able, like the storks, to try again and again. It is not easy to realise this difficulty of learning to fly. The first airmen found their rate of thinking too slow. For all earthly actions they could think quickly enough; but when they came to pass through the air they found the sending of a command from their brains to their limbs was not done fast enough. They found they could not rely upon _thinking_ what to do when a craft threatened to fall. They had to practise until they acquired the power of making a balancing movement without thinking at all; they learned, that is to say, to keep their equilibrium by sub-conscious movements--or, to use a simpler word, by “instinct”; to balance themselves as they passed through the air, like a man balances himself when he rides a bicycle, without giving the action a thought. Lilienthal probed all these difficulties, and saw that--as with other problems--it was not so much brilliant daring that would bring him success, as a painstaking course of practice, along right and sensible lines. So, whenever the weather was favourable and the wind not too high, he made his running leaps down the sides of hills, being content as a rule, in all his early trials, if he remained only a second or so in the air. Here, indeed, was another difficulty of learning to fly. No experience was possible unless a machine was in flight; and yet, in making his first tests, Lilienthal had to be content with a second’s practice here and a second there; to be glad in fact if, after a whole month’s work, he had been for one clear minute in the air. CHAPTER VI “THE BIRD MAN” Construction of an artificial hill--The building of larger craft--Peril of gusty winds--The accident which caused Lilienthal’s death. So determined was Lilienthal to obtain the best conditions for his gliding that, finding no natural slope to meet his purpose, he ordered the construction of an artificial hill. This was built at Gross-Lichterfelde, near Berlin, and was 50 feet high and had gently sloping sides from which, at any direction of the wind, he could make a soaring flight. On the top of the hill, which is illustrated in Fig. 25, Lilienthal had a roomy chamber, and in it he stored his craft. In this illustration, also, the airman may be observed standing upon the hilltop, ready for a trial. By means of dotted lines, and representations of machines in flight, it is possible to show how he glided through the air.