2o6 SCIENCE PROGRESS. 



ment. The ether was purified as much as possible, but in 

 the end the tubes appeared to contain minute quantities of 

 gas which it is very difficult to get rid of. In one of his 

 tubes they were estimated at "000086 and "000026 in the 

 two limbs respectively (in molecules to molecules of ether). 

 Differences as observed by Galitzine, but smaller, appeared 

 to exist. x'\t 195° C. (critical temperature, I94"3°) ^he 

 difference amounted to 4"5 per cent. In a second experi- 

 ment a portion of the permanent gas was transported from 

 the one limb to the other, which now appeared to contain 

 '000029 and "000297 respectively. Again, a difference in 

 density existed above the critical point at 195° C. amount- 

 ing to 19 per cent., but in the opposite direction ; while the 

 difference in pressure was I7"5 mm. mercury in the first 

 case and xyi in the second. The difference of 4 mm. is 

 by no means sufficient to account for the difference in 

 density, which must have been for the greater part due to 

 the small admixture of gas which was transported from the 

 one limb into the other. It is obvious that in an observa- 

 tion of the critical point in a straight tube a similar difference 

 of density may occur, as the liquid and the gas contain dif- 

 ferent percentages of the impurity. As the process of diffusion 

 is a very slow one, one would expect these differences to 

 continue even though the temperature be raised above the 

 critical point, and the phenomena that one would predict 

 this way have a remarkable resemblance to a number of the 

 phenomena actually observed. If the difference in density 

 were due to a difference in the number of liquid molecules, 

 one would expect these differences to be almost instantly 

 equalised by the exchange and rearrangement of the par- 

 ticles, as this process involves no diffusion, only dissociation 

 and association of identical particles. The presence of im- 

 purities would go a long way in explaining also the other 

 abnormalities described above, but there is another important 

 factor to be taken into account — viz., the influence of gravi- 

 tation. This influence had been overlooked until Gouy 

 drew attention to it. It makes the density in the tube 

 different at different levels. The density in one point may 

 be the critical density, while in points above or below it the 



