KING. — MEASUREMENT OF THOMSON EFFECT IN COPPER. 357 



General Description of the Apparatus. 



The copper wire a 5 is soldered into boles in the copper blocks Bj, B2, 

 Fig. 2. A brass tube, T, is slipped over the blocks and the rubber 

 rings r-i, ro, r^, r^. This tube has its sides cut away opposite the wire 

 ah ; but the ends are left whole, so that, by means of them and of the 

 rubber rings, jackets, through which a water circulation can pass, are 

 formed around the copper blocks. The leads, 3, 4, 5, etc. are of no. 40 

 B. & S. copper wire and are fastened to the bar ab hj an electrolytic 

 deposit of copper. These fine leads are led through holes in the part 

 of the brass tube T not cut away, and through a hard rubber strip, R, 

 to copper binding posts on the base board. The small tube t can be 



Figure 2. 



unscrewed and a water jacket, slotted longitudinally to allow the rubber 

 strip R and the fine leads to pass, slipped over the tube T. So that 

 during an experiment the surroundings of the experimental wire can be 

 kept at a constant temperature. The electric current for heating the 

 wire is brought in by the mercury cups in the ends of the blocks Bi, Bg. 

 Copper leads are clamped on these blocks at E^ and Eo and are con- 

 nected to the resistance boxes A and B and cylinder potentiometer as 

 shown in Fig. 2. One terminal, g.., of a sensitive low resistance gal- 

 vanometer is connected to the movable contact of the potentiometer ; 

 the other, g-^^, can be connected with any one of the leads 3, 4, 5, 6, etc. 



Working of the Method. 



Suppose the wire a b \s heated by the electric current and that the 

 blocks Bi and Bo and the surroundings have reached a steady temper- 



