( 201 ) 



§ 2. Particulars on the comparison and on the investigated wires. In 



these calibrations we have taken the platinum wire which was 

 compared with the hydrogen thermometer in Coram. N" 95 ,: (These 

 Proc. Sept. '06) and which we shall call Pti , as standard. We 

 determined the variation of the resistance of the other wires by 

 bringing them together with Pti at the desired temperature, and by 

 then comparing their resistance with that of Pti . The two platinum 

 wires Ptm and Ptv were brought in the same cryostat (see § 4 

 Comm. 95') together with Pti , and whereas the temperature was 

 kept constant with one resistance according to the indication of the 

 WHEATsTONE-bridge, the ratio of the resistance of the other to Pti was 

 determined by means of the differential galvanometer. Pty was also 

 measured separately with the WHEATSTONE-bridge. The difference of 

 the results by the two methods amounted only to 0,02 °/ at tne 

 lowest temperatures. 



Just as Pti, Ptm and Pty were supplied by Heraeds; they were 

 delivered at the same time, but later than Pti. The diameter of all 

 three was 0.1 m.in. After having been treated and wound round 

 the glass (see Comm. N'. 95 c § 3) in the same way, they were heated 

 for a long lime in an annealing furnace for glass. Ptm and Pty 

 differed only in this respect that after being heated Pty was partly 

 unwound, and then wound again, and was not heated in the annealing 

 furnace again. 



To obtain also a resistance thermometer of very small dimensions 

 a platinum wire of 0,05 m.in. diameter was wound round a tube 

 of 1 cm. diameter and about 8 cm. long. The thin platinum wire 

 was welded to thick platinum wires which were fused in the glass. 

 Consequently the thermometer could be cleaned by means of acids 

 if necessary. The thin wire Ptj used for this thermometer, was also 

 furnished by Heraeus. 



A fourth wire was investigated to get an idea of the 



§ 3. Invariability of the resistance thermometers for low tempe- 

 ratures with the time, viz. the resistance thermometer with which the 

 observations were made by Meillnk in 1902, and which we shall 

 call Pt,\[. The zero point appeared to have remained unchanged to 

 one 300000 l,] ). This was also the case with Pti, after measurements 

 had been made at very low temperatures with the resistance ther- 

 mometer for two years. 



Repetition of the calibration at low temperatures of 1902 did not 



give an equally good harmony. We found: 



l ) The thermometer had got defect in consequence of the bursting of the glass 

 cylindres. However carefully it was repaired, yet this gave rise to a diminution of 

 length of the wire of 3 mm. or 0,030 '/o> for which a correction was applied. 



