CONVERSATION IX. Of Colours. CHARLES. After what you said yes terday, I am at a loss to know the cause of different colours: the cloth on this table is green; that of which my coat is made is blue, what makes the difference in these? Am I to believe the poet, that Colours are but phantoms of the day, With that they're born, with that they fade away; HUGHES. Tutor. These are very appropriate lines, for without light the diamond would lose all its beauty. James. The diamond, I know, owes its brilliancy to the power of reflecting almost all the rays of light that fall on it: but are vegetable and animal tribes equally indebted to it? Tutor. What does the gardener do to make his endive and lettuces white? Charles. He ties them up. Tutor. That is, he shuts out the light, and by this means they become blanched. I could produce you a thousand instances to show, not only that the colour, but even the existence of vegetables, depend upon light. Close wooded trees have only leaves on the outside, such is the cedar in the garden. Look up the inside of a yew tree, and you will see that the inner branches are almost, or altogether barren of leaves.. Geraniums and other green-house plants turn their flowers to the light; and plants in general, if doomed to darkness, soon sicken and die. James. There are some flowers, the petals of which are, in different parts, of different colours, how do you account for this? Tutor. The flower of the hearts-ease is of this kind, and if examined with a good microscope, it will be found that the texture of the blue and yellow parts is very different. The texture of the leaves of the white and red rose is also different. Clouds also which are so various in their colours are undoubtedly more or less dense, as well as being differently placed with regard to the eye of the spectator; but the whole depends on the light of the sun for their beauty, to which the poet refers : But see, the flush'd horizon flames intense MALLET. Charles. Are we to understand that all colours depend on the reflection of the seve ral coloured rays of light? Tutor. This seems to have been the opinion of Sir Isaac Newton; but he concluded from various experiments on this subject, that every substance in nature, provided it be reduced to a proper degree of thinness, is transparent. Many transparent media reflect one colour, and transmit another: gold-leaf reflects the yellow, but it transmits a sort of green colour by holding it up against a strong light. J Mr. Delaval, a gentleman who a few years since made many experiments to ascertain how colours are produced, undertakes to show that they are exhibited by transmitted light alone, and not by reflected light. 7 James. I do not see how that can be the case with bodies that are not transpa rent. Tutor. He infers, from his experiments, which you may hereafter examine for yourselves, that the original fibres of all substances, when cleared of heterogeneous matter, are perfectly white, and that the rays of light are reflected from these white parti cles through the colouring matter with which they are covered, and that this colouring matter serves to intercept certain rays in their passage through it, while a free passage being left to others, they will exhibit, according to these circumstances, different colours.-The red colour of the shells of lobsters after boiling, he says, is only a superficial covering spread over the white calcareous earth, of which the shells are composed, and may be removed by scraping or filing. Before the application of heat it is so thick as to appear black, being too thick to admit the passage of light to the shell and back again. The case is the same with feathers, which owe their colours to a thin layer or transparent matter on a white ground. |