760 
MR. A. McAULAY ON THE MATHEMATICAL 
Thus the former theory explains thermoelectric effects satisfactorily. But we shall 
see that we cannot suppose A zero. Hence we must on the present theory suppose 
that the main thermoelectric effects are reversible, but that there are subsidiary 
irreversible ones that with the present means of experiment it would be practically 
impossible to disentangle from the former. 
90. The detailed comparison between the two theories is most clearly made by 
means of the thermoelectric diagram. From equation (22 a) we see that on the 
theory of irreversibility the thermoelectric power, instead of being U/9, is — TijO. To 
any one who is acquainted with the ordinary thermoelectric diagram, the following- 
statements will be sufficiently obvious from the accompanying figures :— 
Theory of Reversibility. 
Abscissa = 0. 
Ordinate = — thermoelectric power with respect 
to lead 
II (lead) _ _ p 
0 
E = the area marked in fig. 4. 
a — 0V e = PS of fig. 5. 
FT = + area marked in fig. 6. 
n - n 0 = + area marked in fig. 7. 
fe 
[o- — 6R e \a-i d6 = — area marked in fig. 8. 
Jf > 0 
Theory of Irreversibility. 
Abscissa = 6. 
Ordinate = — thermoelectric power with respect 
to lead 
Id (lead) 
0 
+ A. 
E = the area marked in fig. 4. 
a — — 3PR of fig. 5 = - 2PQ - PS. 
Id = — area marked in fig. 6. 
n — n 0 = — area marked in fig. 7. 
re 
[<t] «_} dO — + (area marked in fig. 8). 
ho 
+ 2 (area marked in fig. 4). 
= + (area marked in fig. 7). 
+ (area marked in fig. 4). 
Fig. 4. 
Fig. 5. 
Fig. 
7. 
[In this figure OQ is the 
axis and QS = 3QR.] 
Fig. 8. 
