Thermoelectric Position of Platinoid. 



167 



junctions being indicated on the axis of abscissae. The elec- 

 tromotive forces are given in C.G-.S. units, and must be 

 divided by 10 8 if it be desired to reduce them to volts. The 

 differences of temperatures are given in Centigrade degrees. 

 The direction of the current in each of the cases represented 

 is from platinoid to the second metal of the pair through the 

 hot junction. 



Table I. shows, in the way now well known*, the multiplier 

 at any temperature Centigrade which must be used as factor 

 with the difference of temperatures between the hot and cold 

 junctions, in order to calculate the electromotive force in 

 C.Gr.S. units. The algebraic sign corresponds with that used 

 by Tait, and now adopted by Everett (' Units and Constants,' 

 second edition, 1886). 



Table I. 



Platinoid-platinum 

 Platinoid-aluminium 

 Platinoid-iron . . 

 Platinoid-copper (A) 

 Platinoid-copper (B) 



- 925-M6X*. 



- 985-4-31 x*. 

 -2916 + 0-86 x*. 

 -1246-5-44 xt. 

 -1294-4-88 x*. 



Combining the results of Table I. with those of Tait, reduced 

 by Everett, we obtain the thermoelectric distance of platinoid 

 from lead, taken as zero, at various temperatures Centigrade. 

 If any one of the wires platinum, aluminium, iron, or copper 

 used by us were identical with the wire of the same name 

 used by Professor Tait, we should be able to deduce with 

 exactness the distance of our platinoid wire from his lead wire. 

 This, however, was not the case ; and each of the secondary 

 wires used by us gives us, as it were, a different result. Thus 

 we have : — 



Table II. 



From experiment with platinum . 

 aluminium . 

 iron . . 

 copper (A) 

 copper (B) 



Platinoid to lead. 

 - 986-2-26 xt. 

 -1062-3-92 xt. 

 -1182-4-01 x*. 

 -1110-4-49 xt. 

 -1158-3-93 xt. 



Taking the mean of all of these, with the exception of the 

 result for platinum, which we omit because different speci- 

 mens of platinum are well known to differ thermoelectrically 

 enormously among themselves, we obtain for the thermo- 



* Tait, Edinburgh Roy. Soc. Trans, vol. xxvii. (1873), and Everett's 

 ' Units and Constants/ second edition, 1886 — " Thermoelectricity," 



02 



