479 



pressure-balance, it has to be kept in mind, tijat it consists of the 

 total weight of pislon and imposed weigiits, with llie addition of 

 the atmospheric pressure muiliplied by the functional section. 



The pressure of the atmosphere at Leiden is taken as equivalent 

 to 75,9488 cms. mercurj, one atmosphere being equal to 1,0336 

 kilogrammes. 



5. Measuremenfs and ri'sults. As explained in § 2 tiie meas- 

 urements consisted in (1) a comparison of J/„ and J/,„ with the 

 open manometer, (2) a comparison of the pressure-balance with 

 3/,„ and il/,^„. 



We will first discuss the measurements betiiwen 20 and 60 atmos- 

 pheres carried out ^y means of M^„. 



Before undertaking the comparison of M^o with the pressure- 

 balance we made sure hy means of a comparison of il/,, with the 

 open manometer (fully described in the preceding communication), 

 that the indications of the closed manometer still deserve the con- 

 tidence which had always been given them in recent years. As 

 shown in that communication the result of this comparison was, 

 that since the last comparison ') a few years ago the closed mano- 

 meter had not undergone any change. 



The comparison of i/,, with the pressure-balance was cariied 

 out as follows. The piessure having been adjusted at a chosen value, 

 the pressure-balance was set in rotation and we waited, until the 

 mercury-surface in J/„„ did not change any more. The pressure was 

 in this case transmitted from air to oil and as the pressure-impulses 

 which are due to the setting and keeping in motion of the pressure- 

 balance are only very tardily propagated to J/^o, it appeared possible 

 to turn the pressure-balance without any modification of the position 

 of the mercury-column being noticeable. A reading was taken, wiien 

 the mercury-surface had been constant for a considerable time. 



Table 1 gives the results of two series of measurements. For the 

 measurements of June 22 the pressure-balance was once more carefully 

 centred, as we thought that the adjustment had not been quite 

 perfect. 



The ob.servations marked with an asterisk were calculated by 

 means of Schai.kwi.ik's isothermal and in these observations the 

 manometer has thus not merely been used as an indicator. The 

 concordance between the two kinds of observations appeared, however, 

 to be so excellent, that it was considered unnecessary to establish 



') These Proceedings supra, Cunim N'. 146Ö, § 3. 



