( 784 ) 



and in the dead space has as y>\ see e.g. Chappuis) been generally 

 entered into the calculation as it' it took place at perfectly constant 

 density. 



The error committed in this way, is so slight for the permanent 

 gases for small values of* the dead space, that it manifests itself 

 only in the last of the decimals given by Chappuis. For Chappuis' 

 carbonic acid thermometer, however, it attains an appreciable value 

 (the influence extends here to the last decimal but one), so that it 

 was of importance to examine in how far it is permissible to neglect 

 it. This appears when Chappuis' formula is more closely compared 

 with formula (6) of' XI V. 



The density not being constant, either in the thermometer-reservoir 

 nor in the dead space, on account of the fact that e.g. at low tem- 

 peratures gas passes from the dead space to the reservoir, and pv 

 as well as the pressure-coefficient varies with the density, four 

 approximations are applied in this treatment (two for reservoir ami 

 two for dead space), all giving an error in the same direction. 

 (Adsorption is left out of' account). 



The errors caused by these approximations, are of the same order 

 of magnitude for the reservoir and the dead space, the, first applying 

 to a large volume and a small difference of density, the second to 

 a small volume and a large difference of density. The correction 

 which is to be applied to the determination of temperature on 

 account of these errors, only amounts to - 0°.001 at — 100° for a 

 hydrogen-thermometer with 1000 mm. zero-point-pressure and a 

 dead space of 0.01 V , to somewhat less for lower temperatures, 

 and so it may be neglected below 0°. 



Formula (6) differs from the preceding formula by one correc- 

 tion more, which is independent of the size of the dead space, and 

 which is the result of the variation of density in the reservoir caused 

 by the expansion of the glass. This error is of no importance for 

 the determination of the temperature by the hydrogen-thermometer, 

 but may exercise an appreciable influence in some cases, (cf. § 3). 



The approximations mentioned have also an influence on the deter- 

 mination of' the mean pressure-coefficient. The discussion, perfectly 

 analogous to that for the influence on the determination of the tem- 

 perature, gives -J- 0.00000019 as correction for our thermometer, 

 which remains below the limit of accuracy given in Comm. N°. 60. 

 Hence the value 0.0036627 derived in Comm. N°. 60 for hydrogen 

 at 1090 mm. changes into the corrected value 0.0036629. 



§ 2. We may pass from the temperatures derived in the way 



