Vit FLIGHT 237 
investigations, and his results show that the actual 
variation is far greater than would ever have been 
thought likely. When he measured the velocity at 
intervals of seven to seventeen seconds at an altitude of 
fifty-three feet, it varied from ten to twenty-five miles 
per hour, and the inertia of the anemometer may, as he 
says, have reduced the apparent variability. The greater 
the velocity of the wind, the greater was the fluctua- 
tion. On one occasion he found that a wind blowing 
forty miles an hour would almost in an instant drop to 
a calm. His anemometer once stopped dead for one 
second in a high wind. Another trial, when the 
velocity was measured every second, showed that a 
wind of twenty-three miles an hour may in ten seconds 
rise to thirty-three miles, within ten seconds fall 
again to twenty-three, then in another thirty seconds 
rise to thirty-six. As to the cause or the nature of 
the apparent gusts it is difficult to speak positively. 
It is impossible that the onward movement of a large 
volume of air in motion can be suddenly checked. 
Possibly the irregularity may be due to eddies, the 
anemometer during an apparent lull being really within 
the centre or the back current of an eddy, whereas 
during what seems a sudden gust it is in the eddy’s 
onward sweep. But, whatever the explanation, the 
inequality certainly exists, ready for a bird who has 
the skill to make use of. 
But is the wind blowing over the level plain hori- 
zontal? No one would imagine that it is otherwise, 
1 American Journal of Science, January 1894: “ Internal 
Work of the Wind,” by Professor S. P. Langley. [Since 
published separately. ] 
