the Value of the Pitot Constant, 319 



obtained 0'974 between the limits 10 and 60 ft. per sec, 

 and Stanton *, whose value was 1*08. Stanton's number 

 was obtained tor use in his work on the resistance of plane 

 surfaces in a uniform current of air, and was known by him 

 to be a few per cent, too high. 



During 1903-05 a long series of determinations of K in 

 air by two different methods was carried out by the authors ; 

 but as discordant results were obtained, which at the time 

 received no explanation, the work remained unpublished f. 



The authors have since reinvestigated the question, and it 

 will be shown below that by applying certain corrections the 

 results by the two methods may be brought into agreement. 



In the first method, the pitot was moved at constant speed 

 through stationary air. For this purpose, it was fixed to the 

 end of a revolving arm and connected to one side of a 

 pressure-gauge by a tube leaving the arm at the centre of 

 rotation. The pitot and the arm were at right angles to one 

 another so that the former always pointed along the direction 

 of motion. 



Due to the relative motion of the air and the pitot there 

 will be a pitot pressure P given by 



.-V£ 



where v is in this case the velocity of the pitot. 



At the same time, however, due to centrifugal force the 

 hydrostatic pressure in the arm at the centre of rotation 

 will be below that at the pitot end by an amount p. 



If -j— is the slope of the pressure in the arm at a radius r, 



then dp = pco 2 rdr, 



where a> is the angular velocity of the rotating arm whence 



2 I 7 V 



p = pco rdr=p v 



•J o 



where v has the same meaning as before. The resultant 



* Stanton, Proc. Inst. Civil Eng. 1903. 



t These experiments were first undertaken in collaboration with 

 Professor A. P. Cliattock, who identified himself so much with them that 

 his name is omitted from this publication only at his express wish. The 

 authors take this opportunity of thanking him for the part that he took 

 jn the earlier work and for his guidance in its more recent stages. 



