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IX. A Method of Determining the Thermal Conductivity of 

 Copper. By G. F. C. Searlb, M.A. % Peterhouse, Univer- 

 sity Lecturer in Experimental Physics*. 



§1. rpHOUGrH the laws of the conduction of heat are of 

 X importance in a course of instruction in physics, 

 vet the experimental investigation of those laws is. as a rule, 

 thought to be suitable only for advanced students. But, if a 

 substance of very high thermal conductivity, such as copper, 

 he chosen, many of the difficulties fall into the background 

 and then, with suitable apparatus, an elementary student can 

 easilv make an approximate determination of the thermal 

 conductivity in "absolute measure.'" 



The arrangement described in this paper is not well suited 

 for very accurate determinations, since it would be difficult 

 to estimate the proper corrections necessary to allow for the 

 effects of the various imperfections. But in this case, as in 

 many others, if the teacher so designs the apparatus that the 

 corrections are certainly small, he may allow the student to 

 neglect them, and he may be content with knowing that his 

 pupil has gained the leading idea which the apparatus was 

 designed to illustrate. 



The method has been in use for some years at the Caven- 

 dish Laboratory for determining the thermal conductivity of 

 copper : the tact that my students have been interested in 

 the experiment furnishes me with the excuse for publishing 

 an account of it. 



§ 2. The principle of continuous- flow calorimetry is em- 

 ployed in the method. One end of a stout bar of copper is 

 heated by steam, while the other end is kept cool by a stream 

 of water flowing through a narrow copper tube soldered to 

 that end of the bar, and means are provided for determining 

 the temperatures of two intermediate [joints on the bar. 

 When in addition to these two temperatures the difference 1 

 of temperature between the inflowing and outflowing water 

 and also the mass of water flowing through per second are 

 known, the conductivity of the copper is easilv calculated. 



§3. The apparatus is -hown in fig. 1. The copper rod XY 

 i- about 20 cm. long and about 2*5 cm. in diameter. To the 

 end X is fixed a small copper cylinder, closed at the ends, 

 and -team from a small boiler passes through this cylinder. 

 It is convenient to place the boiler below the level of the 

 cylinder, and to make the -team-pipe large enough to allow 

 the water formed by the condensation of the -team to find 



* Communicated by the Author. 



