( -129 ) 



Physics. — "On flic iDedsuveincnt of rery loin fi'injx'i'attin's. 

 A \111. The (k'tcrmliKitioii of the absolute zero according to 

 the h)/dro(/en therniomcti')' of coust<(nt rohiine hikI the reduction 

 of the re(<diiii/.s on the normal hijdroyeti thermometer to the 

 absolute scale.'' Comimuiicatiün N". iOl'' from the Physical 

 Laboratoiy at Leiden by Prof. H. Kameklingh Onnes and 

 C. Braak. 



(Communicated in the meeting of November 30, 1907). 



§ 1. llie determination of the absolute zero. 



D. Bkrtiielot ') has used the observations of Chappuis on tlic 

 pressure coefficients between 0° C. and 100^ C. and the slopes of 

 the ^:>y:-lines at 0° (J. and 100' C. to derive the mean relative 

 pressure coefficient from 0° C to 100^ V. which the investigated gas 

 would possess for densities in the state of Avogadiu), (so we call 

 for shortness the state in which the deviations tVoni the law of 

 Bovle-Gay-Lussac-Avo(tADko may be neglected). In the same way wo 

 may use for this purpose the data of Comm. N". 100^' and Comni. 

 W.m (Sept. J 900). 



If for the pressure coefiicient of the hydrogen thermometer for a 

 zero pressure of 1090 mm. and a density of 1.44 found in Comm. 

 N". 60 we derive the value 0.0036629, we may derive the pressure 

 coefiicient for the state of Avogadro (represented by «av) from the 

 data of Comm. N°. 100^' for B^ for 0" C. and for 100.°20 C. by 

 means of the formula: 



^A„ X 100 «AV -T {Ba,,, - Ba,) ^ 



100X0.0036629 = . (j) 



1090 ^ ^ 



.U. + Ba, -^^ 



where we must replace the value of .Ia„ found in § 3 of Comm. 

 N". iOO'' by a more accurate value: 



.4a„ = 1 - /:?A, - ^ A, = 0.999419 

 and where i)A„„ has been derived from Ba^ and -B.\^,,.,, by inter- 

 polation '). Hence follows for the desired pressure coefiicient 



«AV = 0.0036619. 

 The reverse gives the temperature of the freezing point measured 

 on the absolute scale. Hence: 



1) Sur les thermomètres a gaz. Travaux et Mémoires du Bureau international 

 des Poids et des Mesures, T. Xlll. 



-) In formula (1) the curvature of the ^jy-lines is left out of account, wliich is 

 permissible. 



