JU 



18SB 



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A METHOD OF MEASURING THE PRESSURE AT ANY 

 POINT ON A STRUCTURE, DUE TO WIND BLOW- 

 ING AGAINST THAT STRUCTURE.* 



Francis E. Nipher. 



Various investigations on wind pressures have been made 

 from time to time, by methods which differ essentially from 

 each other. In one form of pressure recorder, an open tube 

 has its mouth directed to the wind by a vane upon which the 

 tube is mounted. The leeward end of the tube connects with 

 some device for measuring the pressure of the air within the 

 tube. This method has been used for a century. 



Newton's idea of this device is very well known, and wind 

 o-auo-es of this kind have been much used. The air stream 

 may be supposed to flow from a reservoir of air of the same 

 density, and having a height h. If the density be d the 

 pressure in dynes per square cm. which would cause the sup- 

 posed efflux at velocity v is 



P^ghd. 



The velocity of efflux is 



V = V 2 g h. 

 Eliminating h 



F=.-v'\ (1) 



If V is given in centimeters per second, and d be given in 

 grammes per cubic centimeter, then P will be given in dynes 

 per square centimeter. At ordinary temperatures and pres- 

 sures, d may be taken as 0.0012. If v be in miles per hour 

 and P be in lbs. per square foot, 



P = 0.0025 v\ (2) 



* Presented to The Academy of Science of St. Louis, December 20, 1897. 



