992 



§2. TJie lieUuin-thermometer. For our measurements we made use 

 of a new gas-lliermometer. In its main points it resembles the type 

 of instrument last used by KAMERLl^GH Onnes and Hoj,st '). We 

 have introduced the improvements which had proved appropriate 

 in the case of the thermometer for measuring temperatures to be 

 obtained with liquid helium, ') as well as others which were 

 suggested by the experience gathered in various measurements in the 

 laboratory. One of the latter consists in the tube of the manometer 

 which is on the side of the thermometer-bulb (the adjustment-lube) 

 and the one which is turned the other way no longer being con- 

 nected by a rubber tube,') but by a glass tube) which involves the 

 adjustment of the mercury by tap /v0, and K0^ (fig. 3 and fig. 4) '') 

 being obtained by means of a mercury vessel D connected to the 

 tube by a rubber tube, air-traps (near tap /i6»,„ and tap K(-J^) being 

 interposed*). The various points are shown") in fig. 1 which gives a 

 general aspect of the thermometric apparatus and which must now 

 replace PI. I of Comm. No. 95^, and in figg. 3 and 4 which give 

 diagrammatic views of the arrangement of the apparatus for our 



n Comm. m 141a. These Proc. XVII (1) p. 501 This type was described for the first 

 time in Comm. No. 27, Zitl. Vers). Akad. Amsterdam, May 1896 as type h. It was 

 used by Kamerlingh Onnes and Boudin Comm. No. 60. (these Proc. 111. p. 299) 

 and afterwards, with only small modifications, by Kamerlingh Onnes and Braak 

 (Comm. No. 95e; these Proc. IX. p. 3G7.) Particulars may be found in the Com- 

 munications quoted. In putting together tlie drawings from Comm. 27, 60 and 95e 

 it should be noted, that even before Comm. No. 60 instead of m fig. 1 PI. II. 

 Comm. No. 27 for the purpose of filling the thermometer a tap like KQtf in fig. 3 

 of the present communication had been fitted to the apparatus (comp. Comm. 

 No. 60; these Proc. Ill p. 299, the end of § 21). 



2) Comm. No. 119. These Proc. XIII, (2) p. 1093 and Comm. 1246. These 

 Proc. XIV (2) p. 678. 



8) The pressure- difference between the inside and outside of the tube in the 

 measurement of the temperatures which are obtained with liquid hydrogen 

 amounts to about 1 atmosphere and at this pressure a rubber tube, even when 

 intended for a high vacuum and of a good quality, transmits air. Moreover the 

 mercury becomes soiled in the long run. a treatment of the tube with caustic 

 soda does not guard against this altogether. And finally the elastic time-action 

 may be troublesome when adjusting to a definite pressure. 



^) An additional figure: fig. 4 has been introduced in the translation. 



^) In this figure some accessories have been introduced in the translation. It 

 remains to be noted that the glass tubes connecting the different apparatus are 

 given diagrammatically and some joints therefore are not shown in the figure. 



^) When the adjustment is accomplished, the tap A'©6 is closed. Any furthei 

 small changes in the adjustment are carried out as in Comm. No. 1246 by means of 

 the adjusting screw fitted for this purpose (comp. fig. 1 and Oi, and o,. on PI. I 

 Comm. No. 119 and fig. 3 o( Comm. No. 1246.) 



