656 SIR DAVID BREWSTER ON THE MOTIONS AND COLOURS UPON FILMS, ETC. 



In the preceding experiments the films were obtained upon apertures in zinc, 

 wood, and card-board, and on small rings of glass, platinum, iron, copper, and 

 brass ; but in the films upon all these substances the phenomena were the same. 

 The films were more persistent when the apertures which they covered were 

 made in plates of greater thickness, and some slight modifications of the pheno- 

 mena arose from the same cause. 



In reviewing the preceding experiments, it is impossible to resist the conclu- 

 sion that the colours have the same origin as those on the soap-bubble. In both 

 cases a colourless fluid issues from the circumference of the film, and spreads 

 itself into rings and coloured bands, which are constantly changing their form 

 and their colour. In some films the colouring matter seems to be occasionally 

 recombined with the film, and the colours to reappear, and vary till the film 

 bursts under the black of the first order. In the soap film the motion of the 

 colouring matter is comparatively languid, but the bands and rings are, to a 

 certain extent, under the influence of gravity, assuming a horizontal position 

 during the rotation of a vertical film ; but some other influence must be sought 

 for, in order to explain the rapid and long-continued play of colours which is 

 exhibited in films of alcohol and the volatile oils. 



