Thermoelectricity of Molten Metals. 501 
TABLE I. 
Lead-Mercury. 
de 
0. p- ao II calculated. 
| Observed. | Calculated. 
200.) 293 | 0 3:4 ‘" 46-2 
100 ee sl 340 4-8 te 13:0 
200 473 920 70 6:5 153°7 
300 573 1710 9-2 83 244-6 
400 673 2640 10:2 10:0 318°5 
500 773 3790 12°5 11:8 448°3 
580 853 4940 19:0 13:2 751-9 
observed value of = and the fifth the value calculated from 
the first two numbers of the fourth column. The differences 
are far greater than possible errors of observation. The last 
column gives the quantities of heat in gramme-calories which 
result at the point of contact of absolute temperature 6, when 
the quantity of electricity electro-chemically equivalent to 
2 grammes hydrogen (193,000 coulombs) passes through. 
If we conclude from the experiments of Le Roux (who, 
however, gives no absolute value of the Thomson-effect) that 
there is no Thomson-effect in lead, there must be such in 
mercury. Moreover its magnitude must be considerable. 
This follows from the observations with the couples HgCu, 
HgPt, HgFe, whose electromotive force I have measured 
for considerable differences of temperature. The Thomson- 
effect is very considerable in the metals Cu, Pt, Fe ; in mer- 
cury it must be at least of equal magnitude according to the 
results of these measurements. ‘ 
The wires employed of the three metals when heated in 
the middle, whilst the ends were maintained at constant 
temperature, gave very considerable electromotive forces 
(70 to 200 microvolts) even after they had been repeatedly 
heated. Mercury on the other hand, as is well known, gives 
none. This last phenomenon, and the Thomson-effect, cannot 
therefore stand in any direct connection. 
In the thermo-element PbHg, the contact-points may have 
the respective absolute temperatures © and @ (O>@); it may 
be supposed to remain closed so long that its thermo-current 
has conveyed the electro-chemical unit of electricity through 
it. Then at the temperature © the quantity of heat II is ab- 
sorbed, and at 6 the quantity of heat Hg is given off to sur- 
rounding objects. The difference Hg—LIg in the present 
