( 176 ) 



soldered to the tube which conveys at an initial temperature of 

 — 190° the compressed helium which is to be cooled down further. 

 This reservoir leads through a steel capillary jV, (as in Comm. 

 N°. 27, May, 1896) to a reservoir iV 4 with stem N s . The quantity 

 of helium and the pressure have been regulated in such a way 

 that the mercury stands in the top of the stem, when the thermo- 

 meter reservoir is quite immerged in hydrogen of 1 5° K, while as 

 soon as the level falls, this is immediately shown by the fall of 

 the mercury. The same purpose is further served by two thermo- 

 elements constantan iron (see Comm. NV 89 Nov. 1903 and N°. 95a 

 June 1906) one on the bottom, the other soldered to the spiral on 

 the same level as the thermometer reservoir. They did not indicate 

 the level in the experiment of July 10 th , because something got defect. 



The evaporated hydrogen contributes in the regenerator Db to save 

 liquid air during the cooling of the compressed helium, and is sucked up 

 (along 15 and He) in the large cylindre of the conjugated methylchloride 

 pump (Comm. N°. 14 Dec. 1894), which otherwise serves in the 

 methylchloride circulation of the cascade for liquid air; it is further 

 conducted through an oil-trap, and over charcoal to the hydrogen 

 gas-holder (Comm. N°. 94/), from which the hydrogen compressor 

 (Qomm, N°. 94/) forces the gas again into the store cylindres. 



To fill the helium circulation the pure helium passes from the cy- 

 lindres R l (see PI. II), in which it is kept, into the gasholder floating 

 on oil (cf. Comm. N°. 94/), which is in connection with the space in 

 which the helium expands when issuing from the cock, a german 

 silver cylindre, in which the upper part of the vacuum glass Ea 

 has been inserted. The gas from the gasholder, and afterwards the 

 cold outflowing helium, which has flowed round the regenerator 

 coil, and of whose low temperature we have availed ourselves in 

 the regenerator Da to save liquid air when cooling the compressed 

 helium, is sucked up by the auxiliary compressor V, and then 

 received in the compressor with mercury piston Q (Comp. Comm. 

 N°. 54). This forces it (PI. II and III) along the conduit: 



a. through a tube Ca which at its lower end is cooled down far 

 below the freezing point by means of vapour of liquid air, and at 

 its upper end is kept at the ordinary temperature. Here the helium 

 is perfectly dried. 



b. through a tube divided into two parts along two refrigerating 

 tubes (in Da and Db), in which it is cooled in the one by the 

 abduced hydrogen, in the other by the abduced helium, after which 

 it unites again. 



c. through a tube Cb filled with exhausted charcoal immerged 



