234 THE STRUCTURE AND LIFE OF BIRDS chap. 



These were by no means so complete as we had 

 hoped they would be, owing to an accident to our ane- 

 mometer. This small instrument, which presents sails 

 like those of a windmill to the wind, and, as it turns, 

 registers the length of the stream of air that has acted 

 on it in the allotted time, was all that was required 

 for the lower levels. 



The place chosen, New Romney sands on the coast 

 of Kent, has exceptional advantages for such experi- 

 ments. There arc no hills or cliffs to tilt the wind 

 upwards, no trees or other obstacles to make it play 

 tricks, so that it was a horizontal wind without com- 

 plications that was experimented on. 



The following are averages made out from four 

 series of experiments : — 



Velocity of the wind 

 Altitude. per minute. 



2 inches 515 feet. 



1 foot 



2 feet 



4 feet 



7 feet 6 inches ... 



736^ 

 770 

 918 

 1,021 



As the wind comes in gusts, it is necessary, if the 

 results are to be trustworthy, to make a number of 

 measurements and strike averages. The figures show 

 that the rate of increase diminishes as you ascend, the 

 difference in velocity at two inches from the ground 

 and one foot being very great. The following are the 

 averages from only two series : — 



Velocity of the wind 

 Altitude. per minute. 



7 feet 6 inches ... ... ... ... 1,375 feet. 



9 feet 6 inches ... ... ... ... 1,457^ „ 



The plan for measuring the velocity of the wind at 



