(77) 



plate the way in which of late we have made the connections for 

 the compression tube for piezometer determinations. 



If we compare this figure with plate I, fig. 1, of Comm. N". 84, 

 March '03, where the same parts are designated with the same letters, 

 and also with the description of it given in Comm. N". 84, then no 

 further explanation is required. The upper end of the level glass C\ 

 is bent in order to immerse C'ji in the oil vessel C\^. The cocks 

 and connections wdiicli are not kept under oil, as for instance C^, 

 are those where a leak must show itself by the outllow of mercury. 



Physics. — Communication N". 94° from the Physical Laboratory 

 at Leiden by Prof. H. Kamekling Onnes. "3Iethoch' and appa- 

 ratus used in the cri/ogenic laboratory. VIL A modified cri/osiat." 



(Communicated in the Meeting of May 27, 1905) 



§ 1. In several Communications I have described cryostats based 

 on the use of baths of liquefied gas e^'aporating at ordinary or lower 

 pressure. For those cryostats where, as described in Comm. N". 14, 

 Dec. '94, I succeeded in maintaining during any desired time a bath 

 of V4 to V2 liter of liquid oxygen for measurements at a constant 

 low temperature by means of a circulation, no vacuum glass at all 

 was used. The whole method had been worked out before Dewar's 

 investigations show^ed that the vacuum glasses were fit above all for 

 storing liquid gases. 



Nor were any vacuum glasses used in the improved cryostats of 

 large dimensions described in Comms. N". 51, Sept. '99, and N°. 83, 

 Feb. '03. When we started the measurements for which these 

 cryostats were used, we could only obtain sufficiently trustw^orthy 

 vacuum glasses which w^ere blown to tit exactly when we were 

 satisfied with small dimensions. 



Since, however, excellent vacuum glasses which are also of large 

 dimensions are made to fit, especially by R. Burger at Berlin, it 

 will be possible in many cases to find vacuum glasses of the proper 

 size and the just mentioned methods of arranging will be especially 

 reserved for those cases where we want vertical walls of j^lane 

 parallel glass, or when the bath must be of excessively large 

 dimensions ^). 



In Comm. N°. 83 III § 6 we have already described a cryostat 

 of small dimensions constructed by means of a vacuum glass. The 



1) Comp. the end of VIII of this Series of Communications. 



6* 



