58 Mr. H. H. Poole on the Thermal Conductivity 



of granite being about the same as that of limestone, we have, 

 putting in these figures, 



W 



o 





here 



W' = W 



■7S 



the various letters having the same meaning as before. A 

 typical determination is shown in Table III., the various 

 columns having the same signification as before. 



Table III. 



The furnace current was turned on at 1U.31 A.M., the 

 choking-coil being short-circuited. The choking-coil was 

 first put in circuit at 12.54 p.m. The central wire current 

 was turned on at 11.21 A.M. 



P.M. 









A. 



V. 



w. 



Bi- 



9 V 



E,. 



0. 



100a. 



W . 



E,- 



A. 



KxlO 



K'xlO" 











12.52 





112 









4309 



15-4 



4488 



336 















12.54 



300 



62 



459 



300 



1377 



... 













268 









1.16 



!t 



58 



459 



3-00 



1377 



4479 



16-0 4665 



347 







629 



























-4 37 



1402 









2.16 



f| 



— 



4-59 



300 



1377 



4429 



16-9 4625 



345 







666 



10-91 i 19 























-237 



13-89 









A 23 



2.52 



ff 



56 



4-58 



300 



L374 



4411 



17*3 46 L 2 



344 







664 



[O-gg 



l 186 























(» 



18-74 







421 



3.45 



It 



60 



4-58 



300 



13-74 



44d7 



17-6 4C.12 



344 



0-88 



13-69 



1 ">7 



10-77 



1 24 



4.52 



„ i 59 



4-5S 



3-00 



1374 



1413 



17-9 462] 



345 







650 



inc.;. i-28 







! 















0-16 



13-73 





\ 245 



5.34 



•• 



58 



4-58 



:;ixi 



1374 



4413 



18-0 4622 



-m:> 







661 





4-215 





Mean value K=4-23x 10" 3 at 345° C. 



A peculiarity noticed with the granite which had not 

 appeared with the limestone, is the apparent rise in the value 

 of K with decrease in \Y. Ii was Eonnd thai this is partially, 

 ;it least, explained by the taet thai a small temperature dif- 

 ference is indicated by the multiple couple when the Eurnace 

 is heated and the temperature steady, no energy being 

 generated in the central wire. Under these circumstances 

 the axis of the cylinder is ai a slightly lower temperature 

 than the outer parts, so thai when only a small quantity of 

 lic;it is evolved in the central wire, the observed value 



IS too low, and BO the apparent value of K LS too high. With 



larger values of W this error becomes unimportant. It was 



