( '^91 ) 



we can only use the determinations of Tj? a vers, Sknter and Jacqukrod.') 



Thev have fonnd : 



l*"^ . for the pressure coefïicient of the lieliuni thermometer at 700 

 rooc— looocn 

 m.m. zero pressure L «i^ J700 = 0.00366255 which agrees with 



rooc— lüOOC-i 



0.0036628 for L «t; J, and 



2"^^ for the difference between the indications of the helium thermo- 

 meter ^[le and the hydrogen thermometer ^u.^ (each of about 1000 m.m. 

 zero pressure) at tlie boiling point of oxygen (^ii^ — ^iie)_i8o°c. = 0°.10, 

 and at that of hydrogen (/u, — ^HiO— ^.^^"c- = 0''.20, which differences 

 are so considerable that Callendar ") concludes thence that the correc- 

 tions of the helium thermometer to the absolute scale are negative. 



The two results which strongly deviate from mine may be readily 

 explained if one adopts that the determination of the coefTicient of pressure 

 variation of helium by Travers, Senter and Jacquerod has not yielded 

 the true value. For if the differences in indication found by them 

 between their helium- and their hydrogen thermometer are reduced by 

 means of the corrections of each of these thermometers to the absolute 

 scale which are given iri Comm. lOO'^ and in Table I of this Comm., to 

 the difference in readings on the absolute scale, which are found at 

 the same temperature by means of the hydrogen thermometer which 

 gives ^11^ and by means of the helium thermometer which gives 

 ^He, there remains at — 182'' a difference 



i^iL — <9He)-i82° = OMO — 0°.049 - 0°.002 = 0^05 

 while by extrapolation of the corrections found to — 217° for — 252° 

 one would find 



(<9h, - 6'He)_252° = 0°.20 — 0M2 - 0°.02 = 0°.10. 



When calculating the temperatures tm^ and ^jHo the investigators 



mentioned have taken the pressure coefficient of the helium ther- 



/ He \ 

 mo.neter I «y I to be equal to that of the hydrogen thermometer 



V ' /Tiaveis 



at the same zero pressure (for 1000 m.m. therefore 0.0036626 

 according to our value of Comm. N'\ 60). If the corrections applied 

 by me are > right that pressure coefïicient must therefore, ^t — 182° 

 in order that é^u^ — ^n^z^O be diminished by 0.0000010 so that 



"'«, = 0.0036616 



1) Phil. Trans. Ser. A. Vol. 200 p. 105—180. Kuenen and Randall (Proc. Roy 

 Soc. Vol. 59) have made a determination, which, being only intended to show 

 whether the helium behaved normally, is not made to the high degree of accuracy 

 which is required for a comparison with isothermal determinations. 



2) Phil. Mag. [6] 5. 1903. 



