( 611 ) 



Physics. — ''On tlw rqnituni of state of a .substance in the neufh- 

 hoarliood of the critical point /iqiti(l-((as. II. Spectrophotonietrical 

 inresti(pitioii of the opalescence of a substance in tke nehjh- 

 hourhood of the critical state", by Prof. H. Kamkrlingh Onnes 

 and Dr. W. H. Keesom. Communicatioii N". J04/> from the 

 Pliysic'cil Laboratory at Leiden. 



() I. Introduction. Tlie spectrophotonietrical investigation-) of the 

 opalescence will have to give an answer to the qnestion how the 

 intensity of the light of a certain wavelength scattered in a certain 

 direction with res[)ect to the incident light antl inclnded in a certain 

 angle of vision, in connection with the polarisation state depends on 

 the temperatni-e and the density of the single snbstance in the 

 neighbourhood of the critical point liqnid-gas (cf. Conim. N". J 04c/, 

 § 4). A tirst quantitative contribution to this investigation is given 

 in this communication "). 



We have confined ourselves in this tirst investigation to the deter- 

 mination of: 



J. for different temperatures the ratio in which the i-ays of light 

 of different wave lengths at the same temperature are scattered in 

 a certain direction ; 



2. the way in which the intensity of tiie light of detinite wave- 

 length scattered in a certain direction and included in a certain angle^ 

 of vision changes with the temperature. 



On the supposition a, that the light emitted by the blue mist is 

 owing to the scattering of the ijicident light in consequence of part 

 of the substance condensing to particles of the same size (e.g. spheres) 

 round centres which are uuiforndy spread through the space, the 

 results of the investigation mentioned under 1 will enable us to 

 form an opinion on the size of these particles'), that under 2 on 

 the way in which the total quantity of substance which has condensed, 

 varies with the temperature. 



M This investigation was cariied out before the interesting article of Smoluchowski 

 Ann. d. Phys. (4) '25 (I'^ebr. 7, 11108) p. 205, appeared. We still had an oppor- 

 tunity, however, to compare it with some parts of the text (cf also the preceding 

 (Jommunication). [Added in the English translation]. 



-) The colorimetric determinations of Krikdlander, ZS. physik. Qliem. 38 (1901) 

 p, 385 constitute such a contribution for a mixture of two liquids in the neigh- 

 bourhood of the critical point of separation. 



•') Already Frfedlander loc. cit. p. 438 called attention to the importance of 

 such an investigation for the knowledge of the internal structure of the critically 

 turbid media. 



