( 203 ) 



It appears that wires delivered at the same time show the same course 

 with only small deviations. A considerable difference in deformation 

 of the wire has had only a slight influence for Ptv- The great 

 difference with wires delivered at different times points to the fact that 

 the originally used material and the treatment in drawing the wires out 

 decide on the change of the resistance. How great the influence of 

 the treatment in drawing is appears from the comparison of Pjjj and 

 Ptd- They were supplied by Heraeus about the same time and are 

 therefore probably made of platinum of the same degree of purity. 

 Yet the thinner wire Ptd decreases much less in resistance than the 

 thicker one. At the temperature of liquid hydrogen the differences 

 become very large. In view of the results obtained for gold, which 

 have been inserted in the following Communication (N°. 99 c ), the 

 most plausible explanation is this that the admixtures in the platinum 

 of the wires sent by Heraeus, either due to their being less pure by 

 nature or to the way of drawing, were less with the platinum sent 

 later than with that sent earlier. We come back to this in Comm. 

 N°. 99°. Here we may still mention that Dewar's wire gave 0,30521 

 to ours 0,25344 at —182°, and that only the thickest (0,2 m.M.) of 

 Holborn's wires gave a smaller value than ours, viz. 0,21253 to ours 

 0,21786 at —191°. 



§ 5. Calibration formulae for the new wires. Just as for Ptj we 

 have also calculated the constants for each of the wires Ptui and 

 Pty in a calibration formula which is adjusted down to — 21 7° and 

 does not give to great deviations at the hydrogen temperatures. 

 To be adjusted to the hydrogen temperatures too formulae of another 

 form are required. The above mentioned formulae of the form (A) : 



Wi /10' 10' \ 



— = 1 4- o.MO-3 + 6.M0-* 4- c.UO-6 + d[ I 



« o V T (273.09)7 



give for the adjustment which we distinguish by Ar. 



The mean error proved to be greater, for Pt v even considerably 

 greater than in the calibration in Comm. 95 c , which can be ascribed 

 only partly to the indirect method of the determination of the resistance. 



