MR. C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
405 
one of his papers ( loc. cit.) he describes the phenomenon of the “ nappe.” When a jet 
of water strikes normally on a small flat surface it spreads out as an exceedingly thin 
film in free air, in shape somewhat resembling an umbrella. This film is bounded by 
a kind of fringe, where it resolves itself into drops. It was regarded by Savart 
as a modification of the continuous column of the jet, and he showed that the jet 
vibrations are preserved in it. The fringe by which it is surrounded he regarded 
as analogous to the troubled region. 
When the jet is allowed to strike upon a large flat surface the appearances are 
slightly different. The liquid radiates from the point of impact, forming a thin 
circular film, having the jet at its centre. The film adheres closely to the surface, 
when this is capable of being wetted by it, and is bounded by a region in which the 
liquid is piled up, forming a layer many times thicker than the film. In this adherent 
film also the vibrations impressed upon the jet are preserved. 
The electric current may be passed through any portion of the continuous column or 
of the nappe. It is obviously necessary that the fluid constituting the jet should 
have a certain degree of electrical conductivity. Many saline substances in solution 
will confer the requisite conductivity on water; but those substances are to be 
preferred which do not yield solid insoluble products by electrolysis. The most 
suitable liquid is distilled water acidified with ^^th °f its volume of pure sulphuric 
