24 Mr. C. H. Lees on 



From this it is seen that the cooling is represented with 

 great accuracy by the above equation \i n—viyy the specific 

 heat of the bar being supposed constant. 



We have 



•-r = 4o'18 per minute. 



Now m = 644 grams. 



c=-092 

 s = 160 sq. cms. 



Hence h = '000,128 calorics per sq. cm. per second for i°C excess. 



Statical Experiments to determine k. 



In these experiments the uncut bar of about one metre 

 length is heated at one end, and the temperature along it 

 in the "steady state" determined by means of thermo- 

 j unctions. 



The equation (i) reduces for this experiment to the form 



^^.4(4:)=i-^(^-^)- 



where k represents the conductivity at a temperature v ; 

 and V is the temperature of the air under any section. 

 Multiplying through by dx and integrating we have 





'/ ^ dx I 



x^ x^ 



where Xi x^ are the coordinates of any two points on the bar. 



The following table gives the mean of three experiments, 



the integration being performed by mechanical quadrature. 



