BISHOP. — THERMAL CONDUCTIVITY OF LEAD. 



673 



The heat for the inside of the shell is furnished by the storage cells S. 

 This current is measured by the ammeter F, and the fall of potential is 

 balanced against the Carhart-Clark cell H by means of the resistances 

 R x and R 2 and the galvanometer G^ A resistance R 3 of 0.1 ohm con- 

 nected in series with the ammeter provides a means of calibrating the 

 ammeter in position and during readings. The fall of potential at R 3 

 was balanced against that of R x in series with the storage cells S x , this 

 being balanced just before and after against the Carhart-Clark cell H. 



M x , M 2 , M 3 are electric motors for agitating the oil outside the shell, 

 inside the shell, and around the junction T respectively. 



The current from the 220 power mains N furnished heat to the oil 

 outside the shell, while the current from the 110 mains maintained the 

 tank D at constant temperature. 



1 i— v/WWWnJ 



Figure 2. 



Details of Apparatus. 

 1. Shea. 



The shell is in the form of a hollow sphere of cast lead, in the casting 

 of which every precaution was taken to have the lead free from blow- 

 holes and of uniform quality. It is divided into two hemispheres by a 

 plane passing through a great circle of the sphere. A radial hole was 

 provided for the admission of wires to the heating coil, thermo-electric 

 junctions, and also for the shaft to drive the fans on the interior of the 

 sphere. 



The shell was coated by electrolysis with nickel of a uniform thick- 

 ness of about .7 mm. The apparatus as arranged for this is shown in 

 Figure 2. The solution used was nickel-ammonium sulphate made 

 slightly acid with citric acid. 



The nickel wires, six in number, two inside and four outside, were 

 vol. xli. — 43 



