700 



Mr. A. H. D; 



i vis on 



in calories per cm. of the cylinder and " v" the air-velocity : 

 one curve for each value of the diameter (d). They have 

 been re-drawn in fig. 1 in c.G.s. units. The relation between 

 the four curves is not obvious. However, formula (12) 



Fig. 1. 



H 



2-0 



1-5 



10- 



0-5 



a 



CD 

 CO 



o 



5- 

 CD 



0-43 err/. 



cm. per sec. 



dia^' 



V — 



10 



"T o 



15 X 10* 



suggests that they can be replaced by one curve if " H " is 

 plotted against " vd." In fig. 2 this has been attempted 

 from the experimental data *. It is seen that the result 

 is very satisfactory. It is excellent for the three smaller 

 cylinders (0 43-1*93 cm.) and quite good for the fourth 

 (5*06 cm.), although the points of the latter all seem 

 displaced somewhat from the line of the former. 



Possible sources of this displacement may be mentioned. 

 In the "vd" term there is possibility of error in the 



velocity 



<i „ » 



Hughes's method of allowing for lack of 



uniformity of distribution of the air-stream in his channel 

 is open to criticism from a precision point of view. A 



* The points of fig. 1 are too numerous to plot individually in fig. 2, 

 and advantage has been taken of the natural groups (of from 2 to 

 6 points) which occur, and mean values have "been plotted. 



