432 



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

 Fig. 10. 



D 

 O 



difference of density is very great — continually diminishes. We see 

 the reason for this to he that the vortex at the back of the disk since 

 it tends to make the liquid move along its stream lines, will increase 

 the pressure in the rear and thus diminish the resistance. In fact we 

 see that w T hat the vortex does is to make the conditions very much 

 the same as if the saucer-shaped drop were moving in a stream 

 flowing with the same velocity. The existence of the following vortex 

 is shown in a very beautiful manner in the next stages represented at 

 i and k in the figure : the edges of the saucer-shaped disk become 

 thinned out to such an extent by the action of the radial streams above 

 and below, that they are drawn out into fine filaments which imme- 

 diately break up into small spherules, and these are carried round in 

 the vortex behind the drop. 



These latter stages are best shown in the case of a certain solution 

 of oleate of soda let fall into a special sample of paraffin referred to 

 above (p. 426), and the changes are represented in fig. 11. 



If only a small drop of oleate is let fall, the steady state is reached 

 before the spherules are detached, and the drop falls in the shape 

 shown at a. If a slightly larger drop falls, then the form b is reached, 



