LAWS, BISHOP, AND MCJUNKIN. — THERMAL CONDUCTIVITY. 459 



a nickel wire. One junction is fastened securely in a wood fibre plug so 

 that it makes contact with the material of the sphere exactly where the 

 copper joins the iron on the outside. The other junction is placed in a 

 large beaker of oil. The iron wire is cut, and from its terminals, leads 

 taken to a sensitive galvanometer. The beaker is heated until there is 



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FlCiURE I. 



no deflection of the galvanometer, and the temperature read by means of 

 a thermometer. The bath is heated slowly and stirred vigorously to in- 

 sure uniformity of temperature and reduce the effect of the lag in the 

 thermometer. 



The interior of the sphere is filled with oil. The heat is produced by 

 means of an electric heating coil. This coil is made of No. 28 (B. & S.) 

 German silver wire, having a resistance of about 13 ohms. It is wound 



