illustrating the Colours of thin Plates, 377 



spheric pressure 112 pounds to every square inch, I might 

 accomplish my purpose ; I therefore made the following ex- 

 periment. 



Exp. — Having put two ounces of distilled water into an 

 eight-ounce phial, and having added about the size of a large 

 pea of Castile soap, I placed the bottle in a saucepan of 

 boiling water on the fire; the bottle was speedily filled with 

 a dense volume of vapour, which expelled all the air. I now 

 corked it, and after cooling, and thus condensing the vapour, 

 had perhaps as perfect a vacuum as could be formed, even by 

 the best air-pump*. I now held the bottle laterally between 

 my hands, and by means of a circular and brisk motion formed 

 a circular film, on which by resting the bottle on an inclined 

 plane, were formed after a short time all the parallel bands or 

 series of colours in the following order: 1. a white or silvery 

 segment at top; 2. a snufF-colo tired brown inclining at bottom 

 to a deep red; 3. blue; 4. yellow; 5. red; 6. blue; 7. green; 

 8. red; 9. green; 10. red; 11. green. (See Figures, p. 378.) 



After some time a black segment was seen to form at the top 

 of the white and continually to increase in size. After a few 

 minutes the parallel bands increased in breadth, and running 

 into one another only three or four distinct bands were seen. 

 Nothing can exceed the beauty of these colours, equal to those 

 of the rainbow, or theplumage of the tropics: whilst writing this 

 description I have these bands in a bottle before me, feasting 

 my eyes on their beauty. In a few minutes more this black 

 segment or aqueous film occupies, perhaps, half the circular 

 film, and the lower half becomes white tinged with orange. 



If we now incline the bottle towards the experimenter's 

 breast, the saponaceous atoms producing these colours are 

 seen to float in the region of the black or aqueous : when 

 placed again on the inclined plane they fall to the bottom of 

 the films. In some time more the entire film becomes black, 

 and all the colours disappear. 



Having now placed the bottle in a basin of boiling water 

 the evaporation was increased, and the black film soon be- 

 came clothed with saponaceous atoms, which being variously 

 condensed produced all the colours of the clouds when the 

 sun is setting on a summer's evening. On again placing the 

 bottle on the inclined plane the parallel bands were again 

 formed by the attraction of cohesion, and the colours afterwards 

 gave place to the black film. I held the bottle laterally be- 



* This vacuum, we apprehend, may be vitiated by the entrance of at- 

 mospheric air through the cork, indicating the necessity of covering it 

 with cement. — Edit. 



Third Series. Vol. 1 1. No. 68. Oct. 1837. 3 C 



