( 213) 



In the Eecord place with regard to the period before 1858, I 

 think as yet little can be said about it. Whilst the much smaller 

 amplitude found in this period makes it fully justifiable in ray 

 opinion, not to connect the results for that period with the later 

 ones, I dare not deduce anything from the observed epochs them- 

 selves. The results 183G — 1858 are very uncertain on account of 

 the small amplitude and I cannot give an opinion about the 

 certainty of the results of the observations of Pond. 



Physics. — Communication No. 4-1 from the Physical Laboratory 

 at Leiden by Dr. II. Kameullxoii Onnks. „A filandard open 

 niajionieler of reduced linirjht ivith traiitifercnce cf pressure by 

 means of cowprcssed e/cis." 



(Read iu the mcctiug uf Uctober 2'Jtli tiOS), 



§ 1. 'T/ie Principle. In order to make accurate determinations 

 of high pressures to about 100 atmospheres, open mercury-mano- 

 meters are indispensable. If we deduce the pressure from the com- 

 pression of any kind of gas in a closed manometer by making use 

 of the equation of condition of this gas, determinations with open 

 manometers form the basis of the measurements and in making 

 accurate measurements it will prove desirable to test if possible the 

 indications of the closed manometer by comparing them with those 

 of the open manometer. But wherever we want to determine the 

 pressure with greater accuracy than is secured by the equation of 

 condition of the gas with which the closed manometer is filled, there 

 is no other way than making the measurements by means of au 

 open manometer, and tliat Avith an apparatus which admits of a 

 high degree of accuracy. 



The frequent use made of closed manometers ') for the experiments 

 in the Leiden laboratory and the necessity to measure the pressure 

 with great accuracy in the case of some determinations (especially 



') If we can measure a range of pressures in a comparatively short time with great 

 accuracy the graduating of closed manometers after we have filled them becomes so 

 simple that we may omit the measurements from which in other cases the value 

 of the scale is deduced. In principle a closed manometer graduated iu this way, as 

 a measuring-apparatus is e(|ual to the metal-manometer, but it is preferable to the 

 latter in so far as its indications when the necessary corrections are applied, are 

 perfectly reliable and probably much more sensitive. The graduating of the closed 

 manometer after its construction relieves the observer from those determinations timt 

 take up much time and are very uncertain. The accuracy which can be attained iu 

 closed manometers to 100 atmospheres is sufficient for the gauging of ordinary metal- 

 mauonieters, which iu order to be reliable must be tested repeatedly and which are 

 specially used as indicators of operations when employed in accurate measurements. 



