1413 
been observed, gave considerable thermo-power; the legs with the 
smallest thermo-power were chosen as potential wires’). 
There was some indication that the resistance of the mercury in 
narrower tubes falls a trifle less than in wider ones, when the 
tubes are cooled to 4°.25 K. (boiling point of helium). The new 
experiments also raised the question whether the almost sudden 
changes were found at a slightly different temperature of the bath 
in the narrower than in the wider tubes. But all this concerns 
particulars which can probably be explained by differences of crystal- 
lization and of heating by the current. 
That the almost sudden change begins at 4°.21 K.*) and ends 
PABEB IL 
Potential difference of the extremities of mercury threads carrying a current. 
| Current paps ampères |potential difference in microvolts 
eng I| October 1911 | December 1911 
October 1911 | December 1911 1=1X 20cm Fene 
0.49 DX 190 0 
0.510 x 260 0 
0.56 0 
3°.65K. ¢ 0.665 0.5 
0.72 is bi 
0.890 4.7 
1.10 2d 
0.010 0 0 
0.014 10.017 
0.016 ie NEEN 
49 19K: 4 0.020 : 10.36 
0.023 ARO EN 
0.024 4.7 
| 0.028 TAS 
1) It amounted to only 12 microvolts, and this was compensated. The seat of 
these E.M. I". (up to 340 mierovolts) is to be found principally in the portion above 
hydrogen temperature. 
*) This means more precisely 0° 04 below the boiling point of helium. 
92 
Proceedings Royal Acad. Amsterdam. Vol. XV 
