1885.] On the Formation of Vortex Rings by Drops. 435 



better formed from some heights than from others. We have observed 

 many cases, varying the size of the drop, the liquid of which it is 

 composed, and the tension of the surface, and have found that the 

 variations in goodness of the rings — where goodness is judged by the 

 length of path in the liquid — depend on the variations in the shape of 

 the drop at the moment it touches the surface. Curves were plotted 

 out, abscissae being taken equal to the height of fall, and orclinates 

 equal to the depth to which the ring goes without breaking up. The 

 curves show two or more maximum points : the abscissa values for 

 these differ from one another by lengths which may be reduced to time 

 intervals. We find that there is very fair agreement between the 

 intervals so calculated and the periods of vibration of the drop about 

 the spherical form. With small drops of water there are several 

 maxima close together, but more widely separated as the fall gets 

 longer (fig. 13). The equivalent intervals are about of a second, 



Fig. 13. 



whilst the period of vibration of a drop of the size used is about 

 ■fa of a second. With as large drops as can be formed from a tube 

 there are only two maxima separated by an interval equivalent to -fa 



