494 SIR DAVID BREWSTER ON THE COLOURS OF THE SOAP-BUBBLE. 



tints, the colouring matter of various orders having collected themselves into 

 innumerable small circular and irregularly shaped systems of rings, floating on 

 the coloured film. Every successive blast upon the film in this state produces 

 a new general tint, and new microscopic systems of rings. 



All the preceding phenomena take place with convex and concave films, and 

 may be observed in films one-fourth and one-half of an inch in diameter, produced 

 upon test tubes. 



II. On the Production of Revolving Systems of Coloured Rings on the Soap-Film. 



If we place a coloured film horizontally when it is in any of the states 

 described in the preceding experiments, and, through a narrow tube, one-eighth 

 or one-tenth of an inch aperture, blow upon its surface in the direction of a dia- 

 meter AB, Fig. 9, there will be produced two systems of rings, C, D, revolving 

 rapidly round their centres, the system C revolving from right to left, and the 

 system D from left to right. If we now blow in the direction AB, Fig. 10, there 

 will be only one circular system revolving from right to left, and covering the 

 whole surface of the film. If the film is square, or of any other form, the rings, 

 when fully developed, will take the same shape. When there are two systems 

 of rings, as in Fig. 9, the colours upon the rectilineal current AB are very 

 remarkable. 



These rings are produced whatever be the colours on the film, and however 

 irregularly they may be distributed ; and, in general, the two systems will be of 

 different forms and of different colours. If, previous to blowing, however, the 

 colours are in regular bands or in concentric circles, as they may be in films of 

 all forms and in all positions, and if the line of the blast bisects them so that the 

 same colours are on each side of it, then the revolving systems will be similar in 

 form and colour. 



The order of the colours in these systems is very curious. The colours of the 

 first order, or rather the first colours of the first order, occupy the centre of the 

 system, if they are upon the film, the black being in the centre, and the white 

 next to it, and the successive orders in successive rings, the breadth of each ring 

 being proportional to the quantity of colouring matter put in motion. The black, 

 for example, is often a small central spot, and when that colour occupies one- 

 half of the film, and the white the other half, which they often do, as in Fig. 7, 

 the revolving portions may be wholly black on one side of the blast AB, and 

 wholly white on the other. If there is no colour of the first order on the film 

 previous to blowing, the first colour of the second order will occupy the centre, 

 the largest particles of the colouring matter being carried by the centrifugal 

 force to the outer rings of the system. If we continue the blast, the rings will 

 gradually disappear, the colouring matter which formed them having been 

 restored to its colourless state, and recombined with the original film. When 



