Thermo-electric Interpolation Formula?. 477 



The deviations in microvolts and percentages from this 

 equation are given in columns 5 and 6, Table III. 



The exponential equation fitting these data most closely, 

 and coinciding with them at nearly the same points as the 

 others, viz. at about 584° and 1250°, is 



2^=0*57674 r l ' 377 -1310, or 



*=0-57674 t 1 " 8 ", £ = 1310. 



KangeO°tol445°C. 



The deviations in microvolts and percentages are in 

 columns 7 and 8, Table III. 



The logarithmic equation applied to the Holborn and Wien 

 data on A yields 



%e= 2-1682 t 1 ' 2156 , or 

 log % 0=1-2156 log * + 0-36610. 



The deviations are given in the last two columns of 

 Table III. 



Holborn and Wien not only compared the ten per cent, 

 rhodo-platinum couple A directly with the air thermometer, 

 but compared with A seven other couples in which one 

 element was platinum, and the other a rhodo-platinum alloy, 

 the percentage of rhodium being stated respectively as, for 

 C 1 and C 2 , 10 per cent, (these two I have combined under C) , 

 D, 9 per cent., E, 11 per cent., F, 20 per cent., G, 30 per 

 cent., H, 40 per cent. For the present purpose I have com- 

 bined these data, which were differences of E.M.F. between O 

 and A, D and A, &c, with the corresponding E.M.F. of A, 

 and thence have deduced the exponential equations for each 



Table IV. 



Designation 

 of the 



Nominal 

 Percentage 



Rhodium. 



Expon. 



Eq. Constants 



>. 









Alloy. 



m. 



n. 



/3 



mv. 



D 



9 



13671 



1-250 



1517 



C 



10 



0-95596 



1-310 



1485 



E 



11 



081734 



1-336 



1469 



A 



10 



0-57689 



1377 



1305 



F 



20 



0-22865 



1-522 



1167 



G 



30 



0-065990 



1-708 



956 



H 



40 



0-063034 



1-720 



977 



