238 THE STRUCTURE AND LIFE OF BIRDS cwap. 
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! If 
this is really the nature of wind when not. interfered 
with by hills or any irregularities and when there 
is no updraught froma sun-heated surface, there will 
soon be no air left in which Herr Lilienthal, who 
is ambitious to be a modern Dedalus, may try his 
wings. Ifa 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 Fiiegekunst, by Otto 
Lilienthal. (Berlin, 1889.) 
