442 



Mr. C. H. Lees on the Law of Cooling. 







_^v 



T26 





£V' 26 & 



x in feet. 



v. 



fix 



v l 



J CO 





■25 



172-1 



195-4 



656-3 



446 



2-28 



•5 



125-25 



1322 



439-7 



311 



235 



•75 



92-3 



92 



299-4 



220 



2-39 



1-25 



52-0 



47-9 



1453 



113 



2-36 



1-75 



30-35 



29-2 



73-7 



60-8 



209 



2-25 



18-2 



15-2 



38-7 



33 



2-18 



2-75 



11-15 



10 



209 



19-2* 



1-92 



3-75 



43 





616 







4-75 



1-85 





2-27 







5-75 



•7 





•96 







The numbers given in the last column indicate a rise of 

 conductivity with temperature, which agrees with the result 

 given by Mitchell as his most reliable. As the integration 



i 



1-26 



dx 



is performed graphically, no great importance is to be attached 

 to small variations of results. The number 2*28 ought to be 

 increased about 5 per cent., as the index 1*26 in the cooling 

 experiment only holds up to about 100° C. temp. -excess. A 

 close agreement of the values of k with one another is pro- 

 bably not to be expected, on account of the deviation of the 

 isothermal surfaces from planes caused by the insertion of the 

 thermometers into the bar. The method of Forbes would be 

 much improved in this respect if the temperatures were de- 

 termined by thermo-junctions either set in the bar at different 

 points, or movable, such as Wiedemann and Franz used. 



Finally, then, in the general theory we, have the equation 

 of continuity in the form 





^ + 



|0*|) + S(* 





with the condition at surfaces in contact with gas 



kv^r + hv n = 0, 



where n can only be taken — 1 when temperature changes 

 of only a few degrees occur, but where c v and probably 

 /•„ may be taken as constant when changes of temperature 

 of not more than 50° C. occur. 



* liable to an error of about 5 per cent, on account of uncertainty of 

 cooling &c. below 10° 0. excess. 



