477 



The accnrac}' given for the two closed manometers is not only a 

 relative one, but for a large number of points an absolute one as 

 well, seeing that both instruments have been directlj- compared with 

 the open manometer at those points. As to the pressure-balance, 

 neither with respect to the absolute nor to the relative accuracj- 

 was anything known with certainty at tiie beginning of onr invest- 

 igation. It had only been found, that the sensitivity of adjustment in 

 the neighbourhood of a definite pressure is very high and certainly 

 amounts to 0.02V„ or even 0.0i7„- As an instance, the pressuretrans- 

 mission through liquids being used, and the pressure-balance being 

 loaded with 65 kilogrammes, the addition of 10 grammes to that 

 load could be observed on i/,2„ with absolute certainty. The data 

 regarding the accuracy of the pressure-balance which we have now 

 obtained by our investigation will be given further down, when the 

 results are discussed. 



4. The cakulations. The reduction of the indications of the open 

 manometer is very simple in priuci|)le: the various corrections, 

 however, require some care, if an accuracy of 0.01 "/o '^ to be 

 guaranteed. These corrections have all been fully discussed by 

 Schalkwijk in his Dissertation, so that we may confine ourselves to 

 a few remarks. The cori-ection for the weight of the columns of 

 compressed air, which transmit the |iressure from each tube to the 

 next, becomes considerable at the higher pressures. Instead of air 

 hydrogen might be used'), which would yield a double advantage: 

 in the first place the correction thereby becomes ten times smaller 

 and secondly the isothermal for hydrogen at 20° is at present very 

 accurately known up to 100 atmospheres'), so that the correction 

 can be calculated with great accuracy. It is true, that this method 

 requires very pure hydrogen being aA'ailable, in order to be certain 

 of the specific gravity, but at the present time hydrogen prepared 

 in the cryogenic laboratory by distillation is so absolutely pure, that 

 an influence on the specific gravity of traces of admixed air, which 

 is relatively large, need not l)e feared. We have ascertained, how- 

 ever, that for pressures up to 100 atmospheres it is not yet necessary 



1) This method was recommended by H. Kamerlingh Onnes in 1898; comp. 

 These Proceedings 1, p. 213, 1898, Comm. N'. 44. 



2) J. G. Schalkwijk, These Proceedings 3, p. 421, 481, 1901. Comm. N«. (57. 

 These Proceedings 4, p. 23, 29, 35 1901. Comm. N". 70, Dissertation. Amsterdam, 

 1902 II. Kamerlingh Onnes, G. A. Guommelin and Miss. E. I. Smid, These Proceed- 

 ings supra. Gomra. N". 1-I6b. For the temperature correction compare the 

 empirical equation of stale of H. Kamerlingh Onnes in the paper by J. P. Dalton. 

 These Proceedings 11, p. 863, 1909. Comm. N". 109a. 



31* 



