430 Prof. J. J. Thomson and Mr. H. F. Newall. [Dec. 17, 



When the liquid into which the drop falls has been allowed to rest 

 for some honrs, a ring will go much further and will last much 

 longer without splitting up, than when it follows on a succession of 

 rings. Some rings of very dilute permanganate have thus been ob- 

 served to last for as long as ten minutes. 



When there is little difference in the density of the drop and the 

 liquid into which it falls, the ring does not break up until there is no 

 vortex motion in it. 



When, however, the difference in density is large, the ring may 

 break up while it is still rotating. 



If a tube be drawn out into a fine capillary and be filled with sul- 

 phuric acid, and held so that its capillary end is just beneath the 

 surface of a column of water, a fine stream of acid flows down ; and 

 on it marked headings appear. Each bead gives rise to a vortex ring, 

 and the rings so formed behave in characteristic manner (fig. 9.) 



Fig. 9. 



Here there seems strong evidence of a tension between the acid and 

 the water, but the appearances are to be explained by differences of 

 velocity in the stream, brought about by motion in the column of 



