472 



of the top of tlie maiiometerdibe give an explanation, unless this 

 erior were supposed to have been of an amount entirely excluded 

 by the measurements themselves. Nalurall}' it migiit be questioned, 

 whether the term in i^—'^^ left out can represent the course of the 

 isothermais in tiiis region with an accuracy corres|)onding to the 

 accuracy of the observations. Tlie observations in this region are 

 much more accurate than for the lest of the isothermais, the study 

 of which as a wiiole led to the selection of the polynome in the 

 given form for the purpose of representing the complete net of 

 isothermais. The circumstance, that the deviations in the range below 

 60 atmospheres show a systematic change, may possibly be a sign, 

 that the development wiiicli was chosen is actually not quite sufficient 

 for the present purpose. 



In a subsequent paper our observations will be discussed in con- 

 nection with the further, fairly numerous observational data concerning 

 the equation of stale for hydrogen. 



Physics. — "Comparison of a pressure-halance of Schaffer and 

 BuDENBERG vuth tlu'. Open st(indavd-gauge of the Leiden Physical 

 Laborator ij heUoeen 20 and 100 atmospheres, as a contribution 

 to the tlicory of the pressure-balance." By Dr. C. A. CROiMMELiN 

 and Miss E. I. Smid. (Comm. N°. 146c from the Physical 

 Laboratory at Leiden). 



(Communicated in the meeting of June 26, 1915). 



1. Introduction. Object of the investigation. The measurements 

 undertaken to extend the determination of the isothermal of hydrogen 

 at ordinary temperature from 60 to 100 atmospheres, which are 

 described in the preceding communication, afforded a welcome 

 opportunity fur carrying out a comparison planned a long time ago 

 of the pressure-balance of SchXffek and Budenbekg with the open 

 manometer of tlie Physical Laboratory at Leiden. 



In the isotlieruuildeterminations of gases under high pressure 

 undertaken at Amsterdam by Piof. Kohnstamm with the apparatus 

 belonging to the van uer WAAi,s-fund the pressure-measurements 

 are based on the indications of a pressure-balance by Schaffer 

 and Budenberg, and the unit in which the volume of the gas 

 in the observations under high pressures is expressed is also 

 dependent ui)0u the indications of a pressure-balance of that kind. 



