STfiSS OJ? STKAIN. 



The formula employed by Smeaton in the preparation of 

 the foregoing table, and where P = pressure in pounds per square 

 foot of surface and V = velocity of the wind in miles per hour, 

 was P-= 0.0050 F 2 . 



The U. S. Water Bureau uses the same formula except that 

 the coefficient is made 0.0040. 



The coefficient used was determined experimentally by ex- 

 posing squarely against the wind plates of from four to nine 

 square feet of surface and recording simultaneously the velocity 

 of the wind and its resulting pressure. 



The anemometer, the instrument used for measuring wind 

 velocities, gives readings which only approximate the real veloc- 

 ities, the latter being found by correction. The following table, 

 taken from a circular issued by the U. S. Department of Agri- 

 culture, Weather Bureau, gives the recorded or indicated veloc- 

 ities, their equivalent corrected velocities, and the corresponding 

 pressures. 



TABLE OF WIND PRESSURES. 



Prof. C. F. Marvin, of the Weather Bureau, states that ve- 

 locities beyond 50 to 60 miles an hour are not accurately recorded 

 by the anemometer, and that exact information is therefore 

 impossible, although cases are reported where the anemometer 

 has continuously indicated velocities as great as 80 to 100 

 miles per hour, but exact data for interpreting such indications 



