('(Direction of Heat and Similitude. 



701 



Pitot-tnbe reading is proportional to r 2 , whereas the heat- 

 loss from small and large cylinders is proportional to v' 55 

 and r* 7 respectively. So a value of average velocity, as 

 deduced by Hughes, from the mean square velocity obtained 



Fi« 



2-0 H 



1-5 



H <•<> 



05 



0-4- - 2 cm. cfi'aw. ( Hughes.) 

 506 ■ n ( „• ) 



5-08 » « ' ( Carpenter.) 



0-003 -0-015 " « ( Fornr?ul^, 



■Ki'»g.) 



(cm. sec"') x (c rn.) 



x 10* 



vd. 



from Pitot-tube readings, is not strictly applicable. Further, 

 the particular average required depends on which cylinder is 

 in use. It will be noticed that the double series of points on 

 the graph of fig. 2 come where the high-velocity values of 

 the smaller cylinders are plotted near the low-velocity values 

 of the 5*00 cm/ cylinder. One may mention also that 

 experience with wind channels shows that rectilinear stream- 

 line motion is not obtained unless special precautions are 

 taken. The entrance must be of stream-line shape ; 

 special metal honeycomb should be used at the be 

 the channel proper to break up vortices and ensure recti- 

 linear delivery. 



Even if there is actual discrepancy, it is obvious that 

 the law 7 HccF(nl) is approximately true. Unless a better 

 theoretical formula can be advanced, this point is worth 

 emphasis in the form in which results are presented, even 



ing of 



