32 



Mr. H. Frank. Newall on 



point of collision. The jets come from the right, as shown 

 by the arrow. 



The form of the isochromatic curves is more or less con- 

 stant in character, though the colouring of the figures varies 

 with the velocity of the jets and the angle at which they 

 collide ; increase in either of these conditions lowers the order 

 of the colours produced, as is to be expected. There is a 

 certain symmetry in the figure, more marked on the right 

 than elsewhere. I describe a particular case, which may be 

 taken as a sample of the general appearances. 



Starting, then, from the right, close up to the ripples R, 

 there appears green of the fifth order in a straight line per- 

 pendicular to the axis of the jet, as shown at 1. The colours 

 of higher order I have not made out, on account of the ripples. 

 The line 2 is red of fourth order ; line 3 green of fourth 



order ; lines 4 are red of the third order. Here the symmetry 

 in colour ceases. Lines 5 show yellow of the third order ; 

 and line 6 blue of the third order. The curves appear to be 

 drawn in to a point on the left ; but this I take to be an effect 

 due to refraction through the uneven thickness of the flattened 

 jet. These broader bands of colour are bordered at top and 

 bottom by the colours of higher order succeeding very closely 

 on one another, as suggested in the figure by the lines 7 ; 

 and towards the left at the top, 8, there appear rings, which 1 

 imagine are probably seen reflected from within the nearer 

 jet. 



It is necessary to see that the tubes leading the water from 

 the bottles to the nozzles are kept quite still ; otherwise there 

 are irregularities in the velocity of the jets which give rise 

 to flickering in the colours. And in order to keep the con- 

 ditions of collision as nearly the same as possible throughout 

 one set of observations, it will also be found convenient to 

 separate the jets, if they coalesce, by holding an electrified 

 stick of sealing-wax close to either of the jets for a moment. 



Havingthus found means of avoiding changes in the colours, 

 I proceeded to test the effect of gradually increasing from 

 zero an electromotive force across the film of air between the 

 rebounding jets, by connecting the water in the bottles elec- 



