( :]()() ) 



ï*hysicS. — "(hl the ineiLsiin'iih'iil of very low U)iipevatares. Vlll. 

 (yOinparison of the rrsistiuicc of gold iinre iritJi that of 

 platinum umr." \W H. Mkilink. (Conimiiiiicatioii N". 93 

 (eontimied) from the Pliysical T.aboi-atory at Leiden hy Prof. 

 H. Kamkrt.ingh Onnes). 



(Communkïiled in tlic meeting of June 25, 1904.) 



§ '1. The investigation (le.seril)ecl in liiis |ja|)er forms part of the 

 subject mentioned sub 2 in ^ 1 of Comm. N*. 77, Febr. 1902 and 

 had tor ils chief object llie establishment of ihe method of ol)servati()n. 



The i^ohl wire was made of Ihe material kindly given us by 

 j)r. ('. llorrsKMA, ins[)ector and assay-master general of the Mint, 

 according to whom no impnrities could ho detected in it by means 

 of chemical processes, which, with regard 1 o the accuracy of the gold 

 analysis, excludes an imi)urily of nun-c than V.,,,^"/^. The piece was 

 drawn out to a wire of W,, mm. in diameter. , The great length of 

 the w ire used , howevei-, had rendered a soldered joint in the 

 middle necessary. 



§ 2. Arramicment of the loires. The same advantages wdiich made 

 us prefer a naked ])latiiHim wire to one enclosed in a glass tube 

 (cf. Connn. N". 77) exist also when the wire is made of an 

 other metal, though the difticulties, especially Avilh i-egard to the 

 action on the metal, ai-e greatei-. 



The difticulties of the ari-angement increased, however, considerably 

 with metals of such high conductivity as gold, because then the 

 w ire must be so nuu'h longer in order to produce a sufïicient resis- 

 tance. With the first forms that were tried, the metal wii-e lay in 

 a screw-lhread etched on a glass cylinder. But with the longer 

 wire the latitude for the expansion became so gi-eat that it could 

 slip too easily from the screw grooves and thus cause short-circuiting. 

 In order to obtain deeper grooves the glass cylinder w^as coated 

 Avith a paste of oil and carborundum and slowdy spirally moved 

 with a speed of V, or ^'^ mm. The cylinder grinds against an iron 

 or copper disk, which is kept in ra|)id rotation and thus by means 

 of the i-arboniii(liini a groove is ground in the glass. This groove 

 proved to be nuicli deeper than that formed l)y etching^); the wires 

 of 0.1 mm. in diameter were entirely enclosed m it. On a cylinder 

 of 37 mm. diameter and 55 mm. height we could wind more than 

 12 meters of wire. 



^j Luter we have again succeeded in making slill deeper grooves by etching. 



