238 THE STRUCTURE AND LIFE OF BIRDS CHAP. 



when no exceptional cause intervenes, had not Herr 

 Lilienthal tried to prove, by means of a vane working 

 vertically up and down, that its normal direction is 

 upward, at an incline of 3 — 4 to the horizon. 1 If 

 this is really the nature of wind when not interfered 

 with by hills or any irregularities and when there 

 is no updraught from a sun-heated surface, there will 

 soon be no air left in which Herr Lilienthal, who 

 is ambitious to be a modern Daedalus, may try his 

 wings. If a vane under these conditions were to point 

 upwards, it would be more reasonable to regard the 

 fact as an indication of the eccentricity of all vertical 

 vanes, or of that particular one. While at New 

 Romney I had one made for me having for its larger 

 arm a piece of thin deal one foot long by six inches 

 broad, exactly balanced by a lump of lead attached to 

 the shorter arm. It is true that so small a deviation 

 as 3 — 4 would be hard to detect, but this instrument 

 indicated, as far as I could judge, that a wind blowing 

 over a level expanse is perfectly horizontal. Ex- 

 periments on the direction of the wind on, or on 

 either side of, a small barrier had more interest for 

 me. While standing on a bank only two feet high, 

 its tripod lifting it four feet above the bank, the vane 

 pointed decidedly upwards. Five yards to leeward of 

 a bank eight feet high it indicated that the wind blew 

 downwards, making, a large angle with the horizon; 

 there was but rarely an upward gust. Ten yards from 

 the bank the direction was still mainly downward, but 

 with not unfrequent upward movements. At twenty 



1 Der Vogelflug als Grundlage der Fliegekunst, by Otto 

 Lilienthal. (Berlin, 18S9.) 



