120 



Pte. J. A. Hughes on the 



The Pitot-tube determined the wind-velocity at the middle 

 of the channel ; and since an average value of the velocity 

 over the cylinder was required, a determination was made 

 of how the wind-velocity varied along a vertical line through 

 the position of the Pitot-tube. A reading was taken with 

 the Pitot-tube in its ordinary position : then readings were 

 taken for the same wind velocity at different points across 

 the channel. Thus an average value was calculated for the 

 channel, and this was done for different velocities of the wind. 

 A graph was plotted (fig. 1) showing the relation between the 

 Pitot-tube reading at the centre of the channel and the 

 average reading for the section. From this an average 

 value can be read for any value of the axial wind-velocity. 



Fig. 1. 



IS 



to 













<0 



5 









/ 













-Si 











1 



V) 



O 





/ 



















J 







tan 6=1-08 









Average h t 



n mms. 



S /o 



Calibration of Tunnel. 



/S 



The heat lost was determined by finding the weight of 

 water condensed. The arrangement of the steam generator 

 is shown in fig. 2. The boiler A is placed on the top of the 

 channel, and the steam passes into the top of the tube through 

 the water-trap B placed directly over the tube. The whole 

 was shielded from air-currents by an asbestos cover. With 

 cylinders of the largest diameters and with the stream-line 

 tubes, a metallic steam-trap covered with cotton-wool was 

 used, and the tubes were soldered to the bottom of the can as 

 shown in the diagram. 



