( 1094 ) 
to ensure that when an experimental apparatus is introduced into its 
its interior this experimental apparatus would also be surrounded 
with liquid helium. To be certain that this was the case, it was 
necessary that the principle of the original liquefying apparatus should 
not be altered in any way, and, hence, the difficulty that the liquid 
helium would be contained in a spave that is practically closed above 
by the regenerator spiral could not be avoided. But this space destined 
to contain the liquid helium could still be made as large as was 
found permissible from the experience gained with the liquefying 
apparatus. An apparatus was, therefore, constructed to hold a ther- 
mometer reservoir of greater dimensions than the one which had 
been used up till 1909, a resistance thermometer such as was used 
in the investigation of the electrical resistance at hydrogen tempe- 
ratures, a dilatometer of dimensions greater than those given in 
Comm N°. 112, and also a control dilatometer. 
The apparatus is shown in Fig. 1 Pl. 1"). The letters are the same 
as in Pl. II of Comm. N°. 108, and are accented where one of the 
parts has been modified. Moreover, Pl. IL of that Communication 
holds for the helium cycle as far as its use at ordinary pressure is 
concerned. To allow the helium to evaporate under lower pressure 
the tube that leads the gas off from the liquefier is coupled to the 
wide exhaust of a BurckHarpT vacuum pump capable of transplacing 
u 
360 m.* per hour. To follow this operation the part D, and those 
attached to it in Pl. If Comm. N°. 108 must be replaced by the 
modifications shown in PI. Il fig. 1; connection with the pump is 
made through /?, NV, and this is closed by the tap 22; while 23 in 
a bypass allows a fine adjustment of the quantity of the gas. that 
is being removed; 24 and 25 allow the gasometer and the liquefier 
to be independently evacuated (see Pl. Il Comm. N°, 108). 
Besides the changes in the apparatus necessary to enable it to 
contain the measuring apparatus, it remains to be remarked that a 
second helium thermometer Na,, .Va,, Na,, now serves to indicate 
the quantity of liquid hydrogen present in / instead of the two 
thermocouples that were formerly used in conjunction with the small 
helinm thermometer (now .V’,, .V,, .V,). The position of the liquid 
surface in /’ can be ascertained much more easily from the motion 
of the mercury in the capillaries N, and Va, than was possible with 
the more round-about thermocouple measurements ; the liquid hydrogen 
can therefore be used more sparingly, and the tedious preparatory 
work of adjustment necessary for these experiments can be shortened. 
1) The alcohol glass with its attachments (cf. Pl. Ill, Comm. NO. 108) Za is only 
partially shown in the drawing. 
1) 
