the Hot-wire Anemometer. 517 



The table herewith gives the values of a and b for the 

 various values of the electric current employed :— 



Table III. 



Current. C (amps.). R=« — 61og ln V. 



11 R=0-6556-0-18161og 10 V. 



1-2 R=6'7642- 02345 log 10 Y. 



1-3 R=0'8866-0-29321og 10 V. 



1-4 R=l ;0140 -0-3467 log 10 V. 



1-5 R = M3l5-0-38501og 10 V. 



If, instead of expressing the results in terms of the volume 

 of air passing through the pipe, results are expressed in 

 terms of the mean velocity v in cms. per sec. of the air 

 across the section of the pipe, then the relations assume the 

 forms : — 



Table IV. 



Current. C (amps.). ~R=a— blog l0 v. 



1-1 R=0-7238-0-18161og 10 r. 



1-2 R=0-8522-0-23451og 10 v. 



1-3 R=0"9967 -0-2932 log 10 v. 



1-4 R = l- 1442- 0-3467 lpg 10 v. 



1-5 R = 1-2760- 0-3654 log 10 f. 



In Plate XIII. fig. 10 the respective values of a and b in the 

 relation R = a — Mog 10 V are plotted against the respective 

 values of the electric current as abscissa?. The relation of 

 a and of b respectively to the number of cubic feet of air 

 flowing per hour in the tube is seen to be a linear one in 

 each case. The relation of a to V is given by 



« = l-172C-0-6361, 



and that of b to C is : 



&=0-504:0 C-0-3670, 



so that, R the resistance of the wire is related to the electric 

 current flowing in the wire, and the current of air V flowing 

 in the pipe, expressed in cubic feet per hour, by the 

 relation : — 



R=|\L : 172 C-0-6361)- (0*5040 C-0-3670) log V. 



The expression for the resistance of the wire in terms of the 

 electric current, and the mean velocitv of the air across 



