" Laio " in Physical Optics. 



335 



Apparently, these two quantities are inversely proportional 

 as shown in the following table by the comparative constancy 

 of the product /3x«. 



Water. 



Temperature-range. 



,3. 



at. 



/3x«. 



209 to 3°1 



0203 



•00025 



•0000505 



31 „ 56 



0144 



•0004 



•0000576 



56 „ 87 



0-082 



•00059 



•0000482 



87 „ 94 



0067 



•00072 



•0000482 



In reading this table the approximate character of the 

 value for /3 must be kept in mind. The last column then 

 indicates the probability of some connexion between /3 and a.. 

 a. is calculated from data given by Thorpe. 



Slight though this evidence may appear it seems to me 

 to warrant farther careful investigation, in view of the 

 desirability of finding some method of obtaining a general 

 law governing the thermal expansion of liquids, and the 

 admitted difficulty of the problem. 



Note. — I have quite recently calculated the value of ft 

 from another series of figures due to Ketteler, and quoted in 

 Landolt and Bornstein's tables. The general tendency is as 

 above, but the product /3 x a, varies from *0 4 428 to '0 4 600. 

 There is perhaps internal evidence, however, for regarding 

 the figures as less accurate than the foregoing, so that I let 

 the matter stand, subject to correction. 



Summing up the general results obtained so far, we find: — 



1. In simple liquids the quantity /3 lies between narrow 

 limits, the average being O05 cubic centim. 



2. The ratio fijv averages 0*064. That is, the actual 

 volume of the molecules is about 6 per cent, of the 

 apparent volume. 



3. Liquids known to have exceptional physical properties, 

 such as water &c, give higher values of /3 than usual. 

 This higher value changes with temperature, and is 

 probably a measure of molecular complexity. 



4. There is reason to think that some liquids, like carbon 

 disulphide, yield a constant value for (3 at different 

 temperatures, 



