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Physics. — On the measurement of very loio temperatures. X. 

 Coefficient of expansion of Jena (jlass and of platinum hetio een 

 -j- 16^ and —182°." By Prof. H. Kamerlingh Onnes and 

 J. Clay. Coniiniinication N°. 95^ from the Physical Laboratory 

 at Leiden. 



(Communicated in the meeting of June 30, 1906). 



§ 1. Introduction. 



The difference between the coefficients a and h in the expansion 



r i ^ f ^ \) -^ 



formula for the linear expansion ^ = ^o ^ + k' tttt; + ^^ I tttt: ) P^^ 



and k^ and h^ in the formula for the cubic expansion 



^1 ' 100 ^ ' Viooy i 



between O"" and — 182° found by Kamerlingh Onnes and Heuse 

 (comp. Comm. N". 85, June '03, see Proceedings of April '05) and 

 those found by Wiere and Bottcher and Thiesen and Scheel for 

 temperatures above 0° made it desirable that the strong increase of 

 b at low temperatures should be rendered indubitable by more 

 accurate measurements ^). 



In the first place we have made use of more accurate determi- 

 nations of the variation of the resistance of platinum wires with the 

 temperature (comp. Comm. N". 95*^', this meeting) in order to substitute 

 more accurate temperatures for those given in Comm. N°. 85, which 

 served only for the calculation of a preliminary formula, and then 

 to calculate by means of them new values for a and b which 

 better represent the results of the measurements than those given in 

 Comm. N^ 85. 



By means of the formula 



Wt = W, (1 + 0,00390972 t — 0,039801 t'), 



which holds for the kind of platinum wire used in Comm. N". 85, 



we have arrived at the following corrections : 



in table IV read — 87°,14 instead of — 87°,87 



and — 18r,42 „ „ — 182°,99 



in table V read - 86°,98 „ „ — 87°,71 



and — 18r,22 „ „ — 182°,79 



1) That the coefficient of expansion becomes smaller at lower temperatures 

 is shown by J. Zakrzewski by measuremenis down to — 103°. This agrees with the 

 fact that the expansion of most substances above 0^ is represented by a quadratic 

 formula with a positive value of b. Our investigation refers to the question whether 

 b itself will increase with lower temperatures. 



14* 



