I 2<S Thermal Conductivity of Copper. 



thermal units per second, where K is the thermal con- 

 ductivity. 



Equating this to the former value, we have 



K- m 03-04 

 At ' 6,-6,' 



§5. It has been assumed in this calculation that all the 

 heat which flows across the section of the bar at U flows also 

 across the section at V, and that the whole of this heat is 

 absorbed by the cooling water. To obtain a practical 

 approximation to this ideal condition, the whole bar with 

 its fittings is very thickly wrapped from end to end with a 

 woollen covering. AYool is also wrapped round the copper 

 tubes E, F and round the vessel G. It is not necessary to 

 wrap up the vessel H, as this vessel is in practice at nearly 

 the atmospheric temperature. For convenience, the appa- 

 ratus, when wrapped with the wool, is placed in a wooden 

 box provided with feet. 



On account of the high conductivity of copper and the 

 large cross-section of the bar, the heat conducted along 

 the bar is very large compared with that which escapes 

 altogether from the bar and with that which passes from 

 one end of the bar to the other by conduction through the 

 woollen covering. 



§ 6. To illustrate the working of the apparatus, I give the 

 numerical details of an experiment in which two different 

 rates of flow of water were used *. 



A = 5*267 cm. 2 7 = 9*95 cm. 



M = 250 grms. 



(a) 1 = 82°-OC., 2 =44°-8C., 3 =23°-lC., 4 = 12°-5O. 



£=155-5 sees. 



jr 250x9-i);3 10*6 Qfi . 

 Hence K= -^-77= — r-^ _ . .,-=->) ■= , bbo. 



0-257 x 155'5 372 



(/,) 1= 8O°-8(J., 2 =4O°-9C., 0,=17°-3C, f? 4 =12 -8C. 

 £=65'6 sees. 



Hence K= 5-267x65-6 ' 39-9 = ' 812, 



In obtaining these results it was assumed that the readings 



* In some copies of the apparatus which have been made, the bar is 



II inches in diameter and the internal diameter of the cooling-tube is 

 3-5 mm. The bar is made thicker to diminish the relative importance 

 of the unavoidable errors. 



