144 Mr. A. R. McLeod on the Lags of Thermometers. 



6. Numerical lie suits for Thermometers moving through 

 the Air at Aeroplane Speeds. 



The following approximate expression for the surface 

 conductivity, h, has been derived from experimental data, 

 referring to the case of air moving with a uniform velocity 

 of V miles per hour past the thermometer: 



h= -0000515 V. 



This expression holds only for ordinary aeroplane speeds of, 

 say, 60-100 miles per hour. Taking G = '032°C. per s«c. 

 and V = 60 m.h p., we have the following steady lags for the 

 bulbs already considered (which have each the same volume 

 expansion). 



Table I. — Lags. 



Mercury . 



J 



.. K=-0197, 



« 2 = -0437. 





Shape and 

 Dimension. 



Internal lag. 



Surface lag. 



Total lag. 



Sphere, c= 1 cm 



Qc 2 

 o« 2 



9 =l°-56 



c 



1°61 



j Cylinder, c= 36 cm. 

 j Length = 10 cm. 



ear 



e c = -84° 



•S5° 



Alcohol . . . 



. K = -00043, 



a = -0009026. 



Sphere, c = '55 cm. ... 



£-■*• 



»*- - 91 ° 



l°-62 



Cylinder, c=145 cm. j 

 Length = 10 cm. J 



£■=<- 



e c = -36° 



•45° 



The thanks of the author are due to Dr. G. F. 0. Searle 

 for his kind assistance in revising this paper for publication, 

 and in checking the formulge. 



