810 



Mr. F. B. Youns 



the 



The possibility of making the zone of transition form at 

 varying heights (v. Section C. 4) in the tube also seems to 

 point to the inadequacy of the explanation of Gouy. 



E. Influence of Difference of Temperature. 



The experiments to be described were practically repe- 

 titions of Villard's experiments with ethylene. By passing a 

 current of electricity through the coil N (fig. 4) it was 

 possible to raise the temperature of the upper half of the tube 

 slightly above that of the lower half. In the experiments 

 which were carried out with tube XIV. the lower limit of 

 the coil was about 3 cm. above the top of the plunger. The 

 variations of optical density in the ether were observed, when 

 possible, by means of a strip of squared paper placed behind 

 the vapour jacket. The appearance of the lines when viewed 

 through the tube maintained at a temperature slightly below 

 6 e is shown in figure 5 A ; the vertical lines are sharply 



Fig. 5. 









1 



-J 





--L 









[ ! 



!tw+ ! 



i 1 



! 



— |-)-r 









SIS 



M-Vfl 



A 



B. 



broken at the meniscus. If the temperature is raised rapidly 

 to some point above 6 C the broken verticals become connected 

 by a curve as shown in B ; the curve gradually spreads 

 upwards and downwards, and at the same time the upper and 

 lower portions of the lines gradually open and close respec- 

 tively until their appearanee is uniform throughout. When 

 the presence of opalescence made the observations difficult or 

 impossible, the degree of uniformity of density of the ether 



