Theory of Colours — trans. Charles Lock Eastlake (1840)
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The translator’s English as printed (Charles Lock Eastlake). The original-language text is not held; names are romanised as the translator printed them.
As in the above cases we required an infinitely narrow space between two surfaces which are in contact, so we can consider the pellicle of the soap-bubble as an infinitely thin lamina between two elastic bodies; for the appearance in fact takes place between the air within, which distends the bubble, and the atmospheric air.
463.
The bubble when first produced is colourless; then coloured stripes, like those in marble paper, begin to appear: these at length spread over the whole surface, or rather are driven round it as it is distended.
464.
In a single bubble, suffered to hang from the straw or tube, the appearance of colour is difficult to observe, for the quick rotation prevents any accurate observation, and all the colours seem to mix together; yet we can perceive that the colours begin at the orifice of the tube. The solution itself may, however, be blown into carefully, so that only one bubble shall appear. This remains white (colourless) if not much agitated; but if the solution is not too watery, circles appear round the perpendicular axis of the bubble; these being near each other, are commonly composed alternately of green and red. Lastly, several bubbles may be produced together by the same means; in this case the colours appear on the sides where two bubbles have pressed each other flat.
465.
The bubbles of chocolate-froth may perhaps be even more conveniently observed than those of soap; though smaller, they remain longer. In these, owing to the heat, an impulse, a movement, is produced and sustained, which appears necessary to the development and succession of the appearances.
466.
If the bubble is small, or shut in between others, coloured lines chase each other over the surface, resembling marbled paper; all the colours of the scale are seen to pass through each other; the pure, the augmented, the combined, all distinctly clear and beautiful. In small bubbles the appearance lasts for a considerable time.
467.
If the bubble is larger, or if it becomes by degrees detached, owing to the bursting of others near, we perceive that this impulsion and attraction of the colours has, as it were, an end in view; for on the highest point of the bubble we see a small circle appear, which is yellow in the centre; the other remaining coloured lines move constantly round this with a vermicular action.
468.
In a short time the circle enlarges and sinks downwards on all sides; in the centre the yellow remains; below and on the outside it becomes red, and soon blue; below this again appears a new circle of the same series of colours: if they approximate sufficiently, a green is produced by the union of the border-colours.
469.
When I could count three such leading circles, the centre was colourless, and this space became by degrees larger as the circles sank lower, till at last the bubble burst.
470.
Fifth condition.--Very delicate pellicles may be formed in various ways: on these films we discover a very lively play of colours, either in the usual order, or more confusedly passing through each other. The water in which lime has been slaked soon skims over with a coloured pellicle: the same happens on the surface of stagnant water, especially if impregnated with iron. The lamellæ of the fine tartar which adheres to bottles, especially in red French wine, exhibit the most brilliant colours, on being exposed to the light, if carefully detached. Drops of oil on water, brandy, and other fluids, produce also similar circles and brilliant effects: but the most beautiful experiment that can be made is the following:--Let aqua fortis, not too strong, be poured into a flat saucer, and then with a brush drop on it some of the varnish used by engravers to cover certain portions during the process of biting their plates. After quick commotion there presently appears a film which spreads itself out in circles, and immediately produces the most vivid appearances of colour.
471.
Sixth condition.--When metals are heated, colours rapidly succeeding each other appear on the surface: these colours can, however, be arrested at will.
472.
If a piece of polished steel is heated, it will, at a certain degree of warmth, be overspread with yellow. If taken suddenly away from the fire, this yellow remains.
473.
As the steel becomes hotter, the yellow appears darker, intenser, and presently passes into red. This is difficult to arrest, for it hastens very quickly to bright blue.
474.