( 593 ) 



^ 2. Apparatus. In the liisl pluco a lew words about the arran- 

 gement of the experiments. 1 1 was ilie same for the experiments 

 withont and with the magnetic ticld. Tlie crystals, fixed with wax on a 

 small piece of platinum foil a, {a.^, a^ fig. 3", PI. I), which was carried 

 by a rod a^, were immersed in liquid hydrogen in a double-walled 

 tube (h fig. 2, fig. 3"), which is the continuation of a non-silvered 

 vacuum glass b^, which contained licjuid hydrogen and which 

 is surrounded by another double-walled (r-,,,, c^^) tul)e c, also the 

 continuation of a non-silvered vacuum glass with liquid air, on 

 which it rests on pieces of cork />,. A clearance of \/, mm. between 

 the two glasses (fig 3") proved sufficient to allow the liquid air to 

 circulate along the hydrogen tube. This protects the hydrogen so 

 efFectiveiy from access of heat that the evaporation is insignificant, 

 even when the two tubes are [)laced between the hot coils of the magnet 

 and the crystal is exposed to strongly concentrated electric light. 



The walls of the narrow part of the tubes are very thin, and because 

 the radiation of heat is independent of the distance of the walls they 

 have been i)rought to an exceedingly small distance from each other 

 (0.5 mm.), but without being anywhere in contact. Owing to the 

 skill of Mr. Kesselring, glassblower of the laboratory, who succeeded 

 in doing this, we had at our disposal a tube of 4 mm. inner diameter 

 filled with liquid hydrogen, protected by a tube of liquid air, the 

 outer diameter of which is no more than 8 mm., which allows us 

 to bring the poles of the magnet so near together that very strong 

 fields are obtained even with hollow poles. V. 



The hydrogen tube must be closed hermetically. For this purpose 

 it is fastened in a cap, d, which may be adjusted by means of a 

 levelling board, ƒ, with screws and sliding groove. The tube is brought 

 from below into the cap, where it rests against a wooden cylinder, 

 within d^ (fig. 2), and it is fastened with a thin rubber ring t^i, which 

 lies round d^ doubled over and is turned down when the tube is 

 put in. To ensure tightness a rubber solution is put between ring and 

 glass, and the rubber is pressed tight against the glass and the cap 

 with copper wire. The cap is provided with: 1. the tube r/j^, to 

 which at d^i a head with packing cap d^^ is screwed, in which the 

 rod a^ can turn (by means of a^), and move up and down (by means 

 of the nut r/33). 2. a tube d^ to siphon over liquid hydrogen as 



1) Instead of the usual poles of the Weiss magnet we have used auxiliary 

 pieces, P30 (see figs. 2 and 3), which prolong the cone to a section of 6 mm. 

 diameter, with conic perforations, which have a diameter of 3 mm. on the side 

 of the crystal. 



