44 THE ROYAL SOCIETY OF CANADA 



two sides of the tube, at least not until after prolonged or intense 

 heating. 



Any one performing the Cagniard de la Tour experiment with 

 fairly rapid rise of temperature will notice the great difference in the 

 values of the refractive index in the upper and lower parts of the tube, 

 which values equalize only at higher temperature or after prolonged 

 heating. The experiments of Teichner^ seem to indicate great differ- 

 ence in density in different parts of the tube. Experiments like 

 the above and many others involving questions of solution, of electrical 

 resistance, of optical properties, etc., have led certain writers, notice- 

 ably Traube^ and de Heen,^ to formulate theories which postulate 

 the existence of two kinds of molecules (the so-called liqiiidogenique 

 and gazogenique) and attempt to reduce the abnormalities to a regular 

 trend covered by the theory. In brief, these theories require the 

 existence of what we may call liquid molecules and vapour molecules. 

 The former are congeries of the latter and may produce them by 

 disintegration. The vapour phase in the ordinary two-phase condition 

 is composed of vapour molecules in large numbers and of liquid mole- 

 cules in relatively small numbers. The reverse is true of the liquid 

 phase. As the temperature is raised, the relative amounts of these 

 two kinds of molecules change so as to become more nearly equal, 

 and at the critical temperature they are present in approximately 

 equal proportions. Hence the phases become identical, but not 

 homogeneous in the strictest sense. At the critical point and above 

 it the liquid particles continue breaking up into the more elementary 

 particles and the change occurs slowly near the critical temperature, 

 but more rapidly at higher temperature. In the hands of Mathias 

 this theory is made to account fairly well for most of the abnor- 

 malities. It has been attacked by Kamerlingh-Onnes and others'* 

 who maintain that the effects seen by these observers are due to gravity 

 and to the presence of impurities. There is no doubt that gravity 

 exerts profound effect on the condition of the substance near the 

 critical temperature, as here the substance is very compressible over 

 a limited region of change of volume; and this fact together with the 

 slow diffusion due to the shortness of the molecular path may account 

 for some of the abnormalities. Then, as Kuenen points out, dissolved 

 gases, produced perhaps during the sealing off of the tube after filling, 

 when some of the substance may be decomposed, will result in an 



1 Teichner. Drudes Ann. 13, 598, 1904. 



2 Traube. Drudes Ann. 8, 269, 1902. 



^ de Heen. Recherches Touchant la Physique Comparée et la Théorie des 

 Liquides, Seconde Partie. 



^ See Kuenen loc. cit. for a résumé of the objections to these theories. 



