1406 
in the measurements a 4 does not yet appear in Oxygen above the 
critical temperature at densities which are 100 times the nurmal. 
From this it seems all the more probable that A only appears for 
oxygen at great densities, and in liquid oxygen can rise to the 
considerable value of 71° as the density rises to 1000 times the 
normal. 
In the accompanying figure our observations concerning gaseous 
oxygen and those of KAMERLINGH Onnes and Perrier which we 
confirmed in our last paper, are combined in a graphic represen- 
tation; the uncertain points near the critical temperature are not 
given. The point of intersection of the line for gaseous oxygen with 
the production of the line for the liquid state, appears to have no 
physical meaning; as we supposed in our last paper, it is due to 
the value of the constants, that the temperature which indicates the 
intersection of these lines happens to be about the ordinary one, at 
which amongst others, the observations of W erss and Piccarp fall, and 
below which as yet no observation had been made for gaseous oxygen, 
(To be continued.) 
Physics. — “further experiments with liquid helium. H. On the 
electrical resistance of pure metals etc. VIL. The potential 
difference necessary for the electric current through mercury 
below 4°.19 K.” By Prof. H. KaMERLINGH ONNEs. Communica- 
tion N°. 183a and 1336 from the Physical Laboratory at Leiden. 
(Communicated in the meetings of February 22 and March 22 1913). 
§ 1. Difficulties involved in the investigation of the galvanic pheno- 
mena below 4.°19 K. In a previous Communication (No. 124c of 
Nov. 1911) we related that special phenomena appeared when an 
electric current of great density was passed through a mercury thread 
at a temperature below 4°.19 K., as was done to establish a higher 
limit at every temperature for the possible residual value of the 
resistance. Not until the experiments had been repeated many times 
with different mercury threads, which were provided with different 
leads chosen so as to exclude any possible disturbances, could 
we obtain a survey of these phenomena. They consist principally 
herein, that at every temperature below 4°.18 K. for a mercury 
thread inelosed in a glass capillary tube a “threshold value’, of 
the current density can be given, such that at the crossing of 
the “threshold value” the phenomena change. At current density 
below the “threshold value” the electricity goes through without 
