^ 612 ) 



On the more general snpposition h, that the opalescence is the 

 conseqnence of differences of densit}' e.g. governed by the statistic 

 efpiilibriuni, which extend over parts of the volume of irregular 

 shape and size, a distance can he pointed out which is connected 

 with the average size of these parts of the volume and so with the 

 substance being more or less coarse-grained in that state, and which 

 determines the optical phenomenon in a similar way as the size of 

 the particles on supposition a. The investigation mentioned under 1 

 will then enable us to judge about this distance. When in future 

 we speak of the size of the light-scattering particles, we shall refer 

 to this distance. Iji this case the investigation mentioned imder 2 

 will teach us something about the mean deviation of the density in 

 these parts of the volume. This too will be implied in future in 

 "the quantity of condensed substance". 



The measurements made by us can, however, be only considered 

 as preliminary ones. As, however, we have to put off the continuation 

 of these measurements for some time, we think that we must not 

 postpone the communication of these provisional results any longer. 



§ 2. The arnuh/cnient of the e.vperlments is represented iji PI. 11 

 fig 1. After having passed through a layer of water the light emitted 

 by the luminous body of the NERNST-lamp N^er (70 HK) is concen- 

 trated by the lenses L^ and L.^ (to an image of ± 1 c.M. height) 

 in the tube Et filled with ethylene ^). 



The light scattered upwards in the direction of the axis of the 

 tube ^) by the cloud is concentrated by means of the system of 



1) This was obtained by distilling over so much from the ethylene circulation 

 of' tlie cryogenic laboratory into the glass tube with cock fused to it, which had 

 been cooled in liquid air, and rinsed witii ethylene, that after the gas phase left 

 above the solid elliylene had been drawn ofT, and tlie tube was heated to the melting 

 point, Vs of it was filled. Then with the cock closed the tube was removed from 

 the ethylene circulation, and fused together at a previously narrowed place while 

 still partially placed in liquid air. When the temperature rose to that of the room, 

 it appeared, wlien at 0^ the rime cleared away, that in the gas space a tliin white 

 deposit was visible on the wall, which evaporated some degrees below the critical 

 temperature of the ethylene. This deposit points to the presence of an admixture 

 which is slightly less volatile than ethylene (cf. Villard, Ann. de chim. et de phys. 

 (7) 10 (J897) p. 389). That it was not visible in the liquid space, probably points 

 to a small difference in refrangibility with ]i(juid ethylene. 



When we stiired, and then slowly cooled the tube to below the critical tempe- 

 rature, the meniscus appeared in the top of the tube. 



'^) The top of the tube is surrounded by a black cylindre in oriler to prevent 

 rays of light received by this part from being reflected upwards, and being thrown 

 into the spectroscope. 



