THERMO-ELECTRIC PROPERTIES OF CHARCOAL AND CERTAIN ALLOYS. 325 
Table II. gives the experiments which show that the temperatures given 
above are those indicated by the M-N deflections against which they stand. 



TABLE II. 
Temperature of Oil Temperature of Oil 
round the M-N Deflection. round the M-N Deflection. 
M-N junction. M-N junction. 
288°1° C. 143 732° C; 82:7 
280°8 140-4 150°2 - 70°5 
273°6 TOO Test yy 141:2 65°7 
266°4 133 132 61:4 
257°5 128 123°9 57°5 
248°6 123-7 107°8 48°5 
239°7 Le) 92:5 39°7 
229-1 113°5 79°2 32:7 
211-2 102°5 66:2 26:2 
2011 Ser 0 100%s 23°7 







When the numbers of Table II. are plotted as abscissae and ordinates, they 
give a straight line from which the temperatures of Table I. are obtained 
graphically. Up to 350° C. the deviation from a straight line has been shown, 
both by Professor Tart’s experiments and our own, to be inconsiderable. For 
higher temperatures, however, the deviation is more appreciable, indicating a 
neutral point for M and N at about a white heat. Accordingly, we do not feel 
warranted in giving the results for the higher temperatures which this experi- 
‘mental method supplies; and in the tables which follow we give those deflec- 
tions only which correspond to temperatures below 400° C. Up to this 
temperature other errors pointed out above are also of extremely small magni- 
tude. As it would require too much space to give full tables corresponding to 
Table II. for all substances which we have investigated, we give for the rest 
simply sufficient data to determine the relation between the deflection and the 
temperature of the heated junction of the M-N circuit. 
In deducing from our observations formule showing the relation between 
the temperatures and the corresponding deflections, we have based upon Pro- 
fessor Tarr’s deduction from theory that the electromotive force of a thermo- 
electric circuit is a parabolic function of the temperature,* a deduction 
which is supported by a long series of experimental facts. We have there- 
fore thought it unnecessary to seék for any other expression for the rela- 
tion between deflection (proportional, of course, to electromotive force) and 
temperature than is given by the expression of the former in terms of the first 
* “Trans. Roy. Soc. Edin.” 1872-3, p. 127. 
VOL, XXVIII. PART II. 4Q 
