Section III, 1918 . [135] Trans. R.S.C. 



The Use of a Simple Form of Pitot-Tuhe Under Open Air Conditions ' 



By a. Norman Shaw, D.Sc. 

 Presented by Prof. L. V. King, D.Sc.,F.R.S.C. 



(Read May Meeting, 1918) 



The following notes concerning the use of a simple form of Pilot 

 Tube anemometer under open air conditions were made as a result 

 of some meteorological observations in connection with Dr. L. V. 

 King's Acoustic Surveys at Father Point in September and October 

 1917.^ The experiments with Pilot Tubes, consisted merely of some- 

 what rough tests, but they are recorded because they provide sug- 

 gestive information about the accuracy and possible use of a simple 

 Tube which could be constructed with ease in any laboratory. 



Two Pilot Tubes, designed primarily to test their suitability 

 for the indication and measurement of gustiness, were employed. 

 They were constructed according to specifications kindly given by 

 Mr. J. Patterson, and each consisted of a U-tube of about 8 mm. 

 internal diameter, with its ends bent both in the same direction at 

 right angles to, and in the same plane as, the U part. One end was 

 open and the other was tipped with a polished brass cylinder having 

 a closed conical end. Round the side of the cylinder were six small 

 holes each slightly less than a millimetre in diameter. The U was 

 half filled with gasoline and was mounted on a stand which cquld be 

 tilled to any desired angle in order to increase the sensitiveness for 

 low velocities. 



It is now generally accepted that the formula, v- = 2 P/p, deduced 

 for this type of Pilot Tube from Bernoulli's theorem for stream line 

 motion in fluids, — where v is the velocity of the wind, P the pressure 

 (in absolute units of force) on the open side, and p the density of the 

 air — may be applied in the interpretation of the observations. ^ The 

 \ 



^See A. N. Shaw, previous article in this number; also Dr. L. V. King's Report 

 to the Hon. Adv. Council of Scientific and Industrial Research on "The Acoustic 

 Efficiency of Fog-Signalling, Father Point Experiments, 1917," in which the 

 meteorological observations are discussed by Mr. J. Patterson and the present 

 writer. 



^Hunsaker, "The Pitot Tube and the Inclined Manometer," Smithsonian Pub- 

 lication No. 2368, p. 27 (1916); Bramwell and Fage, "On the Determination of the 

 Pressure- Velocity Constant for a Pitot (Velocity-Head and Static- Pressure) Tube," 

 Tech. Rep. oj the Adv. Com. for Aeronautics {Brit.), 1912-13, p. 35; Rowse, "Pitot 

 Tubes for Gas Measurement," Pro. Am. Soc. Mech. Eng., April 1913, p. 640. 



