THE THERMAL CONDUCTIVITY OF LEAD. 

 By F. L. Bishop. 



Presented by F. A. Laws, December 13, 1905. Received January 12, 1906. 



The method of determining the thermal conductivity here employed 

 is the modification of the wall method due to Professor F. A. Laws, and 

 the object of this research is to determine the limits of accuracy of that 

 method. 



For a general discussion of the method the reader is referred to the 

 article, "A Method of Determining Thermal Conductivity," by F. A. 

 Laws 1 with F. L. Bishop and P. McJunkin. A part of the apparatus 

 used in this investigation is the same as that used in the previous one. 



General Description of Apparatus. 



A diagram of the apparatus is shown in Figure 1. The shell A is sup- 

 ported at the centre of a large tank filled with oil and can be maintained 

 at any desired temperature. The nickel wires from the two surfaces of 

 the shell are led to the mercury cups a, b, in the box C. A piece of 

 the original lead L is brought from the shell to one of the calibrating 

 tanks D. To this lead wire is electroplated a nickel wire similar to the 

 wires on the sphere ; consequently at T we have a junction exactly 

 similar to the junctions on the shell. The wire is brought to the mer- 

 cury cup c in the box C. This provides a means of determining with the 

 required degree of accuracy the exact temperature of the outside or 

 inside of the shell. 



The wires from the galvanometer G are fastened to the block E, 

 which can be placed in position in the mercury cups a, b, and thus con- 

 nect the galvanometer with the thermo-electric junction on the shell. 

 The deflection of the galvanometer G was calibrated by connecting the 

 terminals E at M with the fall of potential across the standard ohm R 4 , 

 this fall of potential being compared with the Carhart-Clark cell H by 

 means of the resistances R x and R 2 . 



1 These Proceedings, 1906. 



