493 



As Lindkmann's formula can be deduced ') from the principle of 

 similarity, a|)plied lo solid substances, the data mentioned for /c/ can 

 serve at the same time as a comparison of these two metals with 

 respect to that principle. In this com|)arison the change of 6 with 

 the temperature has, however, not been taken into account. 



Physics, — "Furthi'v expi'viini'uU iiHtli. liquid heliiou. 0. On the 

 Dx'itsarement of ver;/ Imo teiitpcr.ifiin's. XXV. Thf determination 

 of the temperatures ir/iich are obtained ivith liquid helium, 

 especially in connection irith measurements of the vapoiw- 

 pressure of helium." By H. Kamkhj^ingh Onnes and Sophüs 

 Wkber. (Comm. 1476 from the Physical Laboratory at Leiden). 

 (Comniiuiicated in the meetitTg of June 26, 1915). 



1. Introduction. In this paper will be given some new deter- 

 minations of vapour-pressures of helium based on more accurate 

 temperalure-measurenicnts, as also a conli'ibntion to the knowledge 

 of tiie correction for tiie Ihermal molecular .pi'essui'e, which lias to 

 be a|i[)lied with conslaiit voliinie-lliermometers for low leiiiperatures 

 with gas under diminished pres.sure, if llic manometer is kept a( the 

 ordinary temperature.") 



This correction was discussed in Comm. 1241) (Dec. 1911) ; an 

 estimate of i(s magnitude, which was necessary to form a judgment 

 of the value of (he temperature-determinations, showed thai ils 

 influence would only exceed the limits of accuracy ihen given, viz. 

 0.1 of a degree, in the measurement of the lowest temperatures. 



The present determinalions of ihe boiling point of helium made 

 widi the aid of a helium thermometer with mercury-manometer 

 arranged for more accurate measurements have enabled us to (est 

 the accuracy of (he (empera(ure-determiuation in the previous series 

 of experiments with li(|uid helium, in which (his point had also 

 been determined. It a|)pears that the diiference of the previous 

 results from the present can be explained by the correcdon for the 

 thermal molecular pressure. This correction remains below (he value, 

 then given for the limit of accuracy. As to the correcdon at the 

 lowest temperatures which were measured, this also appears (o have 

 about the estimated magnitude. The previous measurements are thus 

 as a whole confirmed. 



1) H. Kamerlingh Onnes, Comm. N\ 123 (June '11). 



-) Compare for a dilTeicnt ariangement the concliisiou of §7, Comm. Suppl. 34 

 (Sept. 1913), where the investigation contained in the present communication was 

 also announced. 



32* 



