loir.] 



on Problems in Capillarity 



798 



np the tube. These bubbles soon settle to a succession of flat 

 films, thirty being frequently obtained in such a tube. The films 

 thin down to the black stage in a few hours at most, and slowly 

 descend in the tube during many days, provided the temperature 



AO 



O 



h 



-J 



y 



J 

 J 

 < 



flC 



< 



a. 



u \5 

 J 

 < 

 o 



CO 



35 



30 



25 =* 



20 





10 



4 



Days 



Fig. 5. 



remains constant. They are instantly responsive to any shght 

 alteration of temperature, being so sensitive that the approach of 

 the hand is sufficient to cause movement, from the minute alteration 

 of vapour pressure produced by the small increase of heat radiation. 



