1421 
at the ordinary temperature about 35 2, the sentinel thread B about 
36 @ resistance, the resistance C consisted of five threads in series 
of about 80 2 resistance each and with a combined resistance of 
about 390 2 at ordinary temperature. 
At the boiling point of helium Ws, = 0,01831 2, Wg = 
1.01285 2, We = 0,1773 &. The observations were as shown in 
Table IV. 
We had therefore not succeeded, as had been our intention in 
giving a larger section to A and B than to C, in managing that 
if C should show potential difference, it would do so before A and B 
did it. Only if this had happened it would have been shown that the 
heat that brought C to a temperature above the vanishing point 
was developed inside C. And the potential which now appeared in 
C can again be ascribed to heat conduction through A. The expe- 
riment shows very clearly that accidental circumstances in the 
freezing of the mercury threads play a part in the determination 
of the “threshold value” of the current density, and that in caleu- 
TABLE IV: | 
Resistance of a mercury thread 
just below 4°.20 K. 
xr? = 0.0025 mm? for We 
WsA | WsB | Pe 
Temp. TS A 
current density 2.5 Amp. p. mm2 
in Wo 
40,24 (0.163 2 
4 .234 - | 0.161 
4 230 0.011 0.158 
4 222 0.0078 | 0.0774 
4 .208/00022 0.0025 0.00775 
4 .192) 0 000024 0.000024 
4 185, 0.000012 < 10-8 
current density 12 Amp. p. mm2 
in Wo 
| 
| 
4 185, 0.000071 eer | <10—6 | 
current density 20 Amp. p. mm2, 
in W C 
4 eh! 0.000117 | 0.000048 | 
