s 



C. JBarus — Change of Heat Conductivity on 



In the second method the water circulating in the environ- 

 ment came directly from the hydrant, while warm water cir- 

 culated through FF, below the contiguous plates. After the 

 lapse of sufficient time the upper plate was raised as before 

 and suspended. At the same time the cold water of the envi- 

 ronment was passed through FF, thus making the temperature 

 of the walls surrounding the plate D uniform almost instantly. 



The conditions of cooling may be taken from equation (1) 

 by making the temperature excess of the environment r = 0. 

 The equation reduces to In u'/u=A 1 0(t—t')/3I 1 c 1 . 



Data of this kind are given in Table 2, where dt=t—t' and 

 d log u = "434 In u'/u, and where r is the temperature of the 

 environment and u + r, the actual temperature of the suspended 

 plate. It will be seen that groups of consecutive observations 

 were made after intervals of waiting, and that two independent 

 series are in hand. 





Table 2. 









External i 



conductivity. 



Unifor 



m 



Hot plate 



raised. 







environment. 





Mean. 



St 



S log u 



U + T 



r 



h x 10 1 



hi x 10 1 



°c. 





"O. 



°C. 







© c o 



00 00 GO 



1737 



29-2 



5.6 



1028 



935 



1632 



29-4 



5-6 



966 





1644 



25-7 



5-6 



973 





Pause 23 m 













j 180 



1555 



19-9 



5-6 



914 





( 180 



1559 



18-9 



5-6 



923 





Pause 35 m 













j 180 



1435 



13-9 



5-6 



849 





( 180 



1506 



13-4 



5-6 



891 





j 180 



1653 



29-9 



5-6 



979 



919 



( 180 



1671 



28-0 



5-6 



989 





Pause 23 m 













j 180 



1590 



21'4 



5-6 



941 





I 180 



1563 



20-2 



5 6 



925 





Pause 21 m 













j 180 



1504 



16-4 



5-6 



890 





| 180 



1546 



15-6 



5-6 



915 





Pause 32 m 













180 1343 11-5 5-6 



Mean: h Y — -0000082 + -0000007 u. 



795 



In both series in Table 2, h 1 varies with the temperature 

 excess ; and since these values are better than the data of Table 



1, I have taken the mean equation for h x as appended to Table 



2, for the reduction of the observations below. 



