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Physics. — "On tlie measurement of verij low temperatures. XX. 

 Injiuence of the deviations from the lata of Boyle-Chakles 

 on the temperature measured on the scale of the gas-thermo- 

 meter of constant volume accordimj to observations with this 

 apparatus." By Prof. H. Kamerlingh Onnes ajid C. Braak. 

 Conim. N". 102^ from the Physical Laboraton- at Leiden. 



§ I. In Comm. N". dli' (.Ian. '07) under XV the formula of 

 Chappuis (see Comm. N". 95-^ (Oct. '06) form. (3)) for the cal- 

 culation of the temperatures according to the hydrogen thermometer 

 of constant volume was compared with formula (6) of XIV of the 

 same Communication, in which formula attention has been paid to 

 (he deviations from the law of Boyle, whereas they are neglected in 

 Chappuis' formula. As the result of this comparison we stated there 

 that for a dead space of Yioo the mean relative coefficient of pressure 

 between 0° and 100 is to be increased with 2 units of the 7^1' decimal, 

 and the coefficient of pressure of the hydrogen thermometer at 1090 mm. 

 zero point pressure was, therefore, to be put at 0,0036629 instead 

 of at 0,0036627, a modification which is, however, so slight, that 

 it just coincides with the limit of the errors of observation. We have 

 Just found out that for this calculation inaccurate values of B f'J and 



j5(^)o have been used. New calculations have revealed that the 



difference is much smaller than was stated just now, so that it is to 

 be taken into account only for much higher values of the dead space 

 and, with the exception of carbonic acid, has no influence even on 

 Chappuis' last decimal (the 8'''). That the use of the incorrect B^p) 

 was not detected, was due to the fact that the calculation of 

 neglections indicated in XV had accidentally led to the same result, 

 here, however, because the four corrections, as has been mentioned 

 in XV, had been erroneously taken with the same sign, whereas 

 they almost entirely cancel each other. We shall therefore in future 

 keep to the unchanged coefficient of pressure 0.0036627. 



A consequence of the improved calculation is also that table XVIIl 

 of Comm. N", 97^ (Jan. '07) can be dispensed with. The first two 

 corrections derived in XIV § 3 of the Communication mentioned, 

 now become so small that they fall outside the region of observation. 

 The correction calculated at the end of § 3 becomes somewhat smaller 

 for Chappuis' carbonic acid thermometer than has been given there, 

 viz. — 0.22 X 10-<^, to which another correction of —0.8 )< J-0~' 

 is to be added, if also the expansion by the pressure of the gas 

 is to be taken into consideration. 



