the Value of the Pitot Constant. 



361 



(about 6 inches beneath it). This change had, however, no 

 effect on the results. 



Referring to the part PQR of the pitot tube and its 

 connexions in tig. 1, an uncommutated pressure could arise 

 if the arm P was at a different temperature to the arm R. 

 Such a difference was possible because the air in contact with 

 the water in the tank could quite conceivably differ in 

 temperature from the general air of the room, in which case 

 the arm P would then be affected during the How. This was 

 tested by taking direct and reversed zero readings of the 

 pressure-gauge immediately after the flow had ceased, and 

 before the temperature of the arm P could have changed, 

 appreciably. Sometimes a slight effect seemed to be present, 

 but it was variable in its direction. It might possibly have 

 caused some of the fluctuations which always occurred in the 

 readings. 



Analysis of Results. 



Curves IV as thev stand do not bring out the essential 

 nature of the discrepancies between the observed and the 

 ideal pitot pressures ; a simplification is introduced if, instead 

 of taking the square roots of the pitot pressures, the actual 

 pitot pressures themselves are compared with the squares of 

 the corresponding points on the theoretical parabola — that is 

 to say, with an ideal set of pressures for K = l'OO and constant. 



Tiie results of this analysis are shown in the following table, 



1 



v=6*3cms. P, 



per sec. P 2 



x 



w=110. P, 



P....... 



x 



w=156. P, 



P 2 



x 



0=22-0. P t 



*2 



X 



t;=28-3. P t 



P 2 



x 



r=0 



r=S 



r=5 



r=7 



r=9 



r=ll 



X 



0-30 

 0-43 

 0-65 

 0-90 

 117 



1-4 



i-0 



1-3 

 1-0 



10 



0-7 



06 

 04 



0-5 

 02 



0-3 

 00 



0-3 



0-5 



o-o 



0-4 



3-5 

 3-1 



0-3 



3-2 



27 



0-3 



2-5 

 20 



0-2 



1-5 

 1-2 



0-3 



09 

 0-5 



0-4 



6-4 

 6-1 



0-5 



5-9 

 53 



0-5 



4-7 



4-0 



0-3 



29 



23 



04 



1*5 



0-9 



0-5 



0-8 

 00 



(0-3) 



12-2 

 12-4 



0-6 



11-2 

 10-8 



0-7 



8-6 

 8-1 



06 



5-6 



4-8 



0-6 



2-7 

 1-9 



0-8 

 1-2 



o-i 



(-0-2) 



19-5 

 203 



(0-4) 



17-4 

 1.7-5 



(0-5) 



13-7 



13-3 



08 



90 



7-9 



0-8 



41 



30 



11 



1-6 

 02 



1-3 



(-0-8) 



(-01) 



(0-4) 



1-1 



11 



Phil. Mag. S. 6. Vol. 21. No. 123. March 1911. 2 B 



