30 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 62 



referred to the same standard. Standard air is taken to be dry air 

 under the following- conditions : 



Barometric pressure, 29.921 inches mercury. 



Temperature, 62 degrees Fahrenheit. 



Density, 0.07608 pound per cubic foot. 



Comparison of Pitot Tubes 



Opportunity was taken to compare the National Physical Labora- 

 tory standard Pitot tube, calibrated by Bramwell,* with several forms 

 of tube in use by engineers in the United States. 





T 



14' 



1-- 



« , 



Z3 



-ita 



ir 



301 



\ -Zio* 



3£& 



T ^»^-. , , , — .... 



J.U 



J6 



'JJS 



.2o4 



The tube under investigation was mounted in the center of the 

 tunnel and connected by rubber tubing with a Chattock micromanom- 

 eter. Care was taken to eliminate leaks in the leads, and to point 

 the tube parallel to the axis of the tunnel. A steady wind was then 

 blown through the tunnel and its velocity read from the alcohol gage 

 connected with the side suction plate which had already been cali- 

 brated as described in a previous paper. The velocity from the side 



^ Technical Report of the Advisory Committee for Aeronautics, London, 

 1912-13. 



