of Thermal Conductivity and Emissivity. 285 



temperature required is the excess of temperature of the rod 

 over the air, this was done by merely subtracting the tem- 

 perature of the air at the given moment from that of the rod 

 at the same moment. 



Fio- 1. 



Experiment showed that it was possible to move the iron 

 wire on the rod, and replace it, and obtain the same reading 

 as previously ; thus showing that the resistance of the joint 

 did not appreciably alter. As the galvanometer was made 

 somewhat sensitive, its sensitiveness was tested during the 

 experiments by a Daniell cell passing through a large resist- 

 ance (about 13,000 ohms),, the E.M.F. of the Daniell being- 

 compared with that of a Clark cell. Zero readings were also 

 taken between each deflexion. The readings of the galvano- 

 meter were afterwards standardized, a known difference of 

 temperature being produced between the two junctions, and 

 the deflexions observed. The following table gives an example 

 of a standardization : — 



Point A. 



Point B. 



Diff. of Temp. 



Galv. Defl. 



Diff. of Temp. 



Galv. Defl 



4-56 



3-10 



4-62 



3-18 



11-12 



7-45 



11-19 



7-60 



13-99 



9-36 



13-89 



9-43 



20-29 



1337 



20 34 



13-67 



24-50 



1608 



23-99 



16-06 



29-32 



18-99 



29-54 



19-48 



See fig. 2, which is plotted for these values. 



