90 



Lord Rayleigh on 



[May 15, 



it has freed itself from the mass in front, and thus the resulting 

 spherule acquires a backwards relative velocity, which of necessity 

 leads to a collision. ■ Under ordinary circumstances the spherule 

 rebounds, and may be thus reflected backwards and forwards several 

 times between the adjacent masses. But if the jet be subject to 

 moderate electrical influence, the spherule amalgamates with a larger 

 mass at the first opportunity.* Magnus showed that the stream of 

 spherules may be diverted into another path by the attraction of a 

 powerfully electrified rod. held a little below the place of resolution. 



Very interesting modifications of these phenomena are observed 

 when a jet from an orifice in a thin platef is directed obliquely up- 

 wards. In this case drops which break away with different velocities 

 are carried under the action of gravity into different paths ; and thus 

 under ordinary circumstances a jet is apparently resolved into a " sheaf," 

 or bundle of jets all lying in one vertical plane. Under the action 

 of a vibrator of suitable periodic time the resolution is regularised, 

 and then each drop, breaking away under like conditions, is projected 

 with the same velocity, and therefore follows the same path. The 

 apparent gathering together of the sheaf into a fine and well-defined 

 stream is an effect of singular beauty. 



In certain cases where the tremor to which the jet is subjected is 

 compound, the single path is replaced by two, three, or even more 

 paths, which the drops follow in a regular cycle. The explanation has 

 been given with remarkable insight by Plateau. If for example 

 besides the principal disturbance, which determines the size of the 

 drops, there be another of twice the period, it is clear that the alter- 

 nate drops break away under different conditions and therefore with 

 different velocities. Complete periodicity is only attained after the 

 passage of a. pair of drops ; and thus the odd series of drops pursues 

 one path, and the even series another. All I propose at present is 

 to bring forward a few facts connected with the influence of elec- 

 tricity, which are not mentioned in my former communication. To 

 it, however. I must refer the reader for further explanations. The 

 literature of the subject is given very fully in Plateau's second 

 volume. 



"When the jet is projected upwards at a moderate obliquity, the 

 sheaf is (as Savart describes it) confined to a vertical plane. Under 

 these circumstances, there are few or no collisions, as the drops have 

 room to clear one another, and moderate electrical influence is without 

 effect. At a higher obliquity the drops begin to be scattered out of 

 the vertical plane, which is a sign that collisions are taking place. 

 Moderate electrical influence will now reduce the scattering again to 



* " Proc. Roy. Soc," March 13, 1S79. On the Influence of Electricity on 

 Colliding Water Drops. 



f Tyndall has shown that a pinhole gas burner may also be used with advantage. 



