76é 



Meanwhile we remark, that in Pollitzer's experiments too a distinct 

 deviation from Drbue's curve is to be noticed, in the sense of a 

 decrease of 6 (about 115 — 102) with decreasing temperature, which 

 would be, according to our experiments, very considerable down to 

 helium temperatures ; fuither tlia*, according to Lindemann's formula 

 and by comparison with lead (88), 6 = 61 is to be expected for 

 mercury. 



§ 5. Jhe thermal conductivity. 



— iit^ 



.-J 



Fig. 5. 

 perature was 



The thermal conductivity was determined by means of the appa- 

 ratus, represented in figure 5. A ^^-shaped tube, with double 



walls, and closed at one end, was provided 

 with mercury. The closed branch contained 

 a constantin wire S, insulated by means 

 of celluloid, which made contact with the 

 mercury at the free end. This wire' was 

 used as a heating wire. The current return- 

 ed through the mercury itself by means 

 of a wire, in contact with the mercury at 

 the open end of the tube. The fall of tera- 

 measured with 3 constantin thermometers T^, T^ 

 and jTj consisting of wire of Vso "i™- thickness, w^rapped around 

 a small glass tube. The experimental arrangement is further ex- 

 plained by the diagrammatic figure. All wires were connected to 

 each other by two wires, insulated by thin layers of celluloid and 

 further running free through the liquid helium. 



in consequence of a wrong manipulation during the preparation, 

 the tube had lost a little mercury, so that only the two lower 

 thermometer wires could be used. The heat developed in the heating 

 wire and the difference in temperature thus produced were measured 

 at two ditferent temperatures, the one above and the other one 

 below the point of discontinuity in the electrical resistance. The 

 section of the cylinder of solid mercury amounted to 0.47 cm^ 

 the distance of the thermometers to 5,0 cm. 



At the boiling point of helium the supplied energy was 0,633 

 watt/sec, the difference in temperature produced 0.58; at 3°7 K 0,0365 

 watt sec. and 0,23. 



From this we find for the mean thermal conductivity between 

 4°,5 K and 5°,1 K. ^• = 0.27 cal/cm. see. and between 3°.7 K and 

 3°.9 K: A; = 0.40 cal/cm. sec. 



The thing, which immediately strikes us, is that there is here no 



