Sl'2 Professor Sir James Dewar [Jan. 21, 



demonstration of the colour effects can be made by using the film 

 as a mirror for an intense parallel beam of light condensed from an 

 arc lamp. The reflected light is focused by a simple lens combina- 

 tion, and after reflection at a plane mirror can be seen in full detail 

 on the screen. For this purpose a fllm is blown across the centre of 

 a flask about f) in. in diameter. The Epidiascope affords a con- 

 venient means for the illumination and projection. The film is 

 kept inclined at about 10° or 15" to the horizontal ; in a short 

 time the black, shows as a segment of the circular film, steadily 

 increasing in extent from the top. The sharply defined line 

 separating this black segment from the rest of the film makes it 

 appear as if cut off. The continual movements in the film can be 

 clearly seen. These are extremely complex, and consist largely of 

 streams of liquids of varying thickness. Therefore they appear in 

 a beautiful variegation of colours well contrasted from the general 

 tone of the region of the film across which they move. 



Every local disturbance of the delicate equilibrium is shown by 

 coloured streams or wandering coloured areas of various sizes, usually 

 tending to a circular shape. These, however, by collision or mutual 

 attraction, while moving at different speeds in neighbouring paths, 

 are frequently drawn out into threads and chains which cross the 

 path of another moving circle, and are thus, or otherwise, broken, 

 when a separation takes place into a line of small particles, in the 

 manner of the beads on a spider-web. These motions are most 

 strikingly seen when they cross the black area of a film ; a condition 

 which is readily produced by small local differences of temperature 

 in the Gibbs ring. Then a stream of coloured starlike discs breaks 

 out from the Gibbs layer, and pass like rockets through the Ijlack 

 region, giving a brilliant variety of effects as their many-coloured 

 trails cut and coalesce. 



Mr. W. J. Green, B.Sc, of the Davy Faraday Laboratory, has 

 rendered valuable aid in the Research, and Mr. J. AV. Heath, F.C.S., 

 of the Royal Institution, has also assisted in the experiments. 



