( 205 ) 



investigate how Wiv \\i\\i'u\ lieliiini could Ix; cooled before solidit'icalion, 

 and to reach the lowest temperature hitherto attained. Hut, as was 

 pointed out in that Paper, this arranf^einenl did not a|)pear to allord 

 the recjuisite certainty in its action. 



Experiments upon the electrical resistance of metals at helium 

 temperatures and upon the thermal j)roperties of helium were, there- 

 fore, again made (December lOlOi by introducing the necessarv 

 a|)paratus into the chamber of the helium li(pielier, in which the 

 liquid formed by the ex|)ansion of the gas collected. Hut, as long 

 as a stirrer camntt be used in the helium bath, and with this arran- 

 gement its introduciion would be a matter of the gi'eatest diflicidty 

 one cannot be sure of the nnifornnty of the temperature of the bath 

 which, nevertheless, is a siw <ju,a noii, for accurate temperature 

 determinations. There was couse(piently urgent need for the con- 

 struction of a cryostat ^) which, although still closely connected with 

 the liqnelier, would yet aUow the apparatus which one wished to 

 place in the helium bath to be introduced and still have free and 

 independent exit above. In the present paper a description is given 

 of a cryostat which fidfills the necessary conditions. With this cryostat 

 various experiments have been made including those upon the dis- 

 appearance of the resistance of |)ure mercury (Comm. W. 120 Proc. 

 April 1911 and Comm NM22'^ Proc. May lilll). 



Now that this cryostat is available it is possible to measure the 

 resistance of a mercury thread (Cat.i.kndak's bridge method, ordinary 

 differential galvanometer method, method of overlapping shunts, 

 measurement of fall of potential and current strength) whose four 

 leads connecting with the measuring instruments are also (glass tubes 

 filled with in the lower part solid) mercury up to the point at which 

 ordinary tempei'ature is reached. Moreover, the difficulties attending 

 an investigation of phenomena connected with electrical conduction 

 are diminished, and in this connection an nivestigation is proceeding 

 with a view to ascertaining how far one can, in measuring all kinds 

 of very small potential differences, take advantage of the increase 

 of sensitivity experienced by the current carrier (e.g. fixed coil*), 

 suspended coil, current circuit or string) of the galvanometer when 

 brought to the temperatui-e of liquid hydrogen. Finally, one can 

 attempt to obtain baths giving temperatures between the boiling point 

 of helium and the melting point of hydrogen, which must l)e regarded 

 as of the highest importance for resistances (and perhaps for specific 



1) Gf. also Comm. N". 119, Pioc. March I'Jll A § Ü. 



2) When thus cooled the resistance of a fine wire coil is diminished to that of 

 a thick wire coil. 



J4 

 Proceedings Royal Acad. Arasterdani. Vol. XiV, 



