( 207 ) 



Tlio silvered siphon (ubc Eak (see accompanviiig' figure) vvliicli 

 transfers the liquid lielinni from the vaenuin glass Zv/" of the liqnelier 

 in wliieh it collects lo the vacuum glass of the cryostat *S. — the 

 eryostat glass — is fused to the under part of the vacuum glass 

 Ecd'li^. The lower portion of the vacuum glass of the li(piefier as well as 

 the rising limb of the sij)hon Eak^ are siu-rounded with li(|ui(l air 

 in *S'„ from which they are separated by a goi-man silver case ,S', 

 cemented and consequently immovably attached to the li(|uelier glass 

 at aS'ij. To this case the rii^g ;S'^ whicii cari-ies the crvostat glass ;S'. is 

 also tixed immovablv. When the cryostat glass with its rid)ber i-iiig 

 Sr, is attached to this, and the cover \ with its rubber ring -S'«, is 

 placed over the cryostat chamber, this case forms with the coimecting 

 tube aS's and the cryostat glass S. one closed whole. The same 

 method of connecting by means of rul>bei- rings as was used in the 

 earlier cryostats was again enqtloyed with the li(|uetier, at >S',2 above 

 the cemented junction S^^, and this connei'tion was also provided with a 

 safety envelope, thus ensuring an air-tight sealing of the whole 

 enclosed space. A heliunj thermometer whose german silver reservoir 

 JSfb^ is placed in the liquid helium space indicates the accumulation 

 of liquid hehum which may be transferred to the cryostat cluunber; 

 its steel capillary Nh^ passes along by the spiral A of the helium 

 liquefier and is connected to a stem Nh.^ and a barometer tube; 

 this thermometer is placed alongside the thermometers which indicate 

 the level of the liquid in the hydj'ogen chamber of the liquetier X 

 and N(i (cf. the plate of Oomm. N". 119). 



Along the upper end of the siphon EkIi.^ is laid a co|)per capillary 

 Eal through which is flowing liqnid air and which is wrapped up 

 with the siphon tube in a layer of insulating material; by this 

 means it is ensured that when the liquid helium tlows ([uickly over 

 it takes up but little heat. At the extremity of the siphon Pjali.^, 

 whicli opens into this cryostat glass is a valve Eak, consisting of a 

 stopper plate Eak^ which turns about a horizontal axis and is [)ressed 

 against the opening of the vacuum tube by meajis of the large- 

 pitched worm gear Eak.^. The worm is operated from aboxe the 

 cover of the cryostat l)y turning the handle E(ik\ to which is 

 attached the shaft Eak;^ (made partly of glass) passii»g through the 

 s tufting box Eak^. 



The stirring arrangen)eiit consists of a german silver |Him|) Sh, 

 with valved piston >S/>, and outlet valves Sh^ ; by means of a wire 

 ^ib^ and a soft iron cylinder Sb^, inside the glass tube Sb. the piston 

 follows the course of a magnet ;S'<;/, which is moved u|) and down 



14* 



