BISHOP. — THERMAL CONDUCTIVITY OF LEAD. 675 



mately the temperature at which it was desired to take readings. Then 

 the fans in the cavity of the shell were set in rotation and the current 

 from the storage cells turned into the heating coil. The temperature of 

 the outside was adjusted until it remained constant, then the apparatus 

 was allowed to run constant for approximately two hours, tests being 

 made from time to time to determine when it had become constant. 

 The deflection of the galvanometer was read every two minutes. The 

 ammeter reading was maintained constant by an adjustable resistance 

 which would permit of a very small change in the current. The fall 

 of potential across the heating coil was balanced against the Carhart- 

 Clark cell several times during a run, which was usually thirty-two 

 minutes. The variation in the temperature of the oil surrounding the 

 shell was taken at frequent intervals. The galvanometer was immedi- 

 ately calibrated after the readings had been taken. 



Readings. — The following set of readings illustrates the constancy of 

 the various quantities. The first column gives the actual readings on the 

 galvanometer, the second gives the difference between each two succes- 

 sive readings, i. e. the double deflection, the third and fourth give the 

 current and the ratio from which to determine the voltage. The column 

 marked "Temperature Tank" gives the variation of the temperature 

 with time of the oil surrounding the shell. 



Thermal Conductivity. March 16, 1905. 



