452 



made it possible to extend less care on them than on the prepara- 

 tion of the T/- resistances, so that it is not necessary that tlie 

 resistances siiould be shut off' from the air in a glass tube with 

 helium gas. We used the resistances Pb-^9\9-B, diameter 0,5 m.m. 

 not enclosed in a helium atmosphere, 7^6-1919-/, diameter 0,12 m.m. 



enclosed in a helium atmosphere and Isotope 

 P6-1919-/, in dimensions as much as possible 

 the same as Pb-1919-l and treated in the 

 same wav. 



§ 2. Arrangement of the cryostat. The cryostat 

 with which the experiments were made, is 

 executed by and under the supervision of the 

 chief of the Techn. Dep. of the Cryog. Lab., 

 Mr. G. J. Fi.iM. Roughly speaking, it is the same 

 as that described in Comm. NM246. A charact- 

 eristic of the present cryostat is that objects to 

 be measured aie surrounded by helium vapour 

 A or gas (the latter at very low temperature); by 

 -^ using it, the temperature field between the 

 boiling point of helium (4°, 2 K.) and the 

 lowest temp, obtainable with liquid hydrogen 

 (J4°,0 K.) is bridged over for the first time. 

 For the arrangement see fig. 1. In the entirely 

 silvered vacuum glass A, an also entirely 

 silvered vacuum glass B hangs in an inverted 

 position, ending in a single silvered glass tube; 

 the bell-shaped space inside this glass is the ex- 

 perimental chamber. In this space are found the 

 Th resistances (in fig. 1 there is only one, marked 

 W) and the heliumgas-thermometer lit. The 

 upper end of B opens out outside the cryostat 

 and is connected with the gasholder; B is 

 there provided with a regulating tap K for 

 blowing off (not visible in the drawirjg). The 

 liquid helium comes in through the entrance 

 D, the floater C shows the height of the 

 helium level. If the tap K, leading to the 

 gasholder, stands open, the helium will fill 

 both A and B; at the beginning of the ex- 

 periment measurements can thus be made 

 at the boiling point of liquid helium. If the 



