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



minished image of a candle may be distinctly seen by reflection from its outer and 

 inner surfaces. It is sometimes small, and sometimes the size of a sixpence, in 

 which case it is not visibly lenticular. It sometimes increases by the appropria- 

 tion of all or part of the colouring matter around it, and sometimes diminishes 

 by its conversion into colouring matter, or partially recombining with the film. 



When the circular system of rings, with the lens in its centre, is perfect, it 

 decays in the following manner, as observed in three different films. When there 

 is a green ring of the second order round the lens, eight or ten spots of red begin 

 to form upon the green, as in Fig. 13, and sometimes shoot out into as many 

 red spokes, like those of a wheel, joining the next red ring. The system of rings 

 is now splendid, varying in size and colour. Outside of the spotted ring there 

 are generally two orders of colours. The black is gradually enlarging, and the 

 white, with its enclosed rings, diminishing. The eight or ten spots are now green 

 upon a pale greenish yellow ground. In a minute or so they are purple upon a 

 green ground, then reddish, with white in their centre, and moving about deform- 

 ing the rings of the second order of colours. The while ring has now become 

 yellow, the spots, with tails like tadpoles, and green inside, encroaching upon the 

 second order of colours. The spots are now small, brilliant red, and one or two 

 blue upon a yellowish ground. The blue of the first order is now being covered 

 with white spots, and the black, with a sharp edge, constantly encroaching on the 

 white and other colours. The white is now covered with orange tadpole spots, 

 and the other spots changing their form, colour, and position. The film now 

 burst. 



In another concave film, which was very thin, there were six orders of colours, 

 but no lens. The fifth and sixth orders disappeared by the advance of the others, 

 and the third and fourth, occupying the centre, were broken up by numerous 

 tadpole spots, some of them enclosing different tints. These tadpole spots are 

 collecting, as if into a lens or large grey spot full of rings, surrounded by a green 

 ring, round which is a red one. The film now burst from an accident. 



In a third concave film a lens was beautifully formed within the third order 

 of colours, and surrounded with a bright red ring of the third order, and ten 

 bright green spots on a yellowish ground. The spots varied in colour and number 

 till the film burst. 



In a fourth concave film the changes continued till the whole film was black, 

 the lens floating in the centre, and moving about with the motion of the 

 glass. 



When the concave film is thick, or the colourless fluid copious, the lens is 

 sometimes the size of a shilling, but flat, with a few close and almost invisible 

 rings at its margin. It then diminishes to the size of a sixpence, and takes 

 longer time to pass throughthe changes above described. 



