422 



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



It will be seen at a glance from the figures that the variations are onl y 

 in the unimportant parts, whilst the essential parts are recognisably 

 the same. At the early stages the drop is more or less spherical ; 

 bnt as it descends, it gets flatter and flatter, as we might expect 

 since its motion is resisted, and at one of the stages becomes almost 

 disk-shaped, and passes very quickly from this into the ring- 

 shape. 



This change of shape, we imagine, is due to the presence of the 

 vortex motion, the distribution of rotation in the ring being a stable 

 arrangement of vortex motion, whilst that in the disk is not. The 

 vortex motion in the drop has travelled from the boundary, diffusing 

 according to the same laws as those which govern the conduction of 

 heat, the quantity corresponding to the diffusivity in the conduction of 

 heat being in this case /*//>, where fx is the coefficient of viscosity and 

 p the density of the liquid. If fijp be very small, the vortex motion 

 will not travel far into the drop, whilst if it be large it will all have 

 diffused before the ring has become disc-shaped. In neither of these 

 cases should we expect the disk to change into a ring, and it will be 

 seen later on that as a matter of fact it does not. 



Effect of Dropping one Liquid into another. 



A drop does not always make a ring when it falls into a vessel con- 

 taining liquid. We have tried the effect of letting a drop of one 

 liquid fall into a vessel containing another liquid for a good many 

 substances. The results are given in the following table : — 



Column of Water : — 



Kings are formed when drops of the following liquids are let 

 fall into a column of water : milk, alcohol, blood, aqueous solu- 

 tions of sugar, of gum arabic, of potash, of permanganate of 

 potash, of carbonate of potash, of sodic chloride, of copper 

 sulphate, of nitrate of potash, of oleate of soda, of nitrate of 

 silver, of cobalt chloride, of carbonate of soda, of ammonic 

 chloride, hydrochloric acid, acetic acid, nitric acid, Plateau's 

 soap solution, essence of carraway, solution of iodine in 

 ammonia, solution of fluorescein in ammonia, glycerine and 

 water, sulphuric acid. 

 Globules are formed when drops of the following liquids are let 

 fall into a column of water: carbon bisulphide, chloroform, 

 ether, olive oil, paraffin oil, turpentine. 

 Column of Paraffin Oil : — 



Rings: carbon bisulphide, chloroform, ether, olive oil, turpen- 

 tine, butylic alcohol. 

 Globules : water, alcohol, essence of carraway, glycerine and 

 water, dilute sulphuric acid. 



