[81] Propriétés de l’Acide Carbonique liquide, par M. Thilorier, Annales de Chimie, vol. lx. p. 427. Solidification de l’Acide Carbonique: Ibid. p. 432.
[82] On the Liquefaction and Solidification of Bodies generally existing as Gases, by Michael Faraday, D.C.L., F.R.S., &c.; Philosophical Transactions, vol. cxxxvi, p. 155.
[83] Burns, in one of his most natural and pathetic letters.
CHAPTER VII.
LIGHT.
Theories of the Nature of Light—Hypotheses of Newton and Huygens—Sources of Light—The Sun—Velocity of Light—Transparency—Dark Lines of the Spectrum—Absorption of Light—Colour—Prismatic Analysis—Rays of the Spectrum—Rainbow—Diffraction—Interference—Goethe’s Theory—Polarisation—Magnetisation of Light—Vision—The Eye—Analogy—Sound and Light—Influence of Light on Animals and Vegetables—Phosphorescence arising from several Causes—Artificial Light—Its Colour dependent on Matter.
Light, the first creation, presents to the enquiring mind a series of phenomena of the most exalted character. The glowing sunshine, painting the earth with all the brilliancy of colour, and giving to the landscape the inimitable charm of every degree of illumination, from the grey shadow to the golden glow;—the calm of evening, when, weary of the “excess of splendour,” the eye can repose in tranquillity upon the “cloud-land” of the west, and watch the golden and the ruddy hues fade slowly into the blue tincture of night;—and the pale refulgence of the moon, with the quiet sparkle of the sun-lit stars,—all tend to impress upon the soul, the great truth that, where there is light, organisation and life are found, and beyond its influence death and silence hold supreme dominion.[84] Through all time we have evidences that this has been the prevailing feeling of the human race, derived, of course, from their observation of the natural phenomena dependent upon luminous agency. In the myths of every country, impersonations of light prevail, and to these are referred the mysteries of the perpetual renewal of life on the surface of the earth.
This presentiment of a philosophic truth, in the instance of the poet sages of intellectual Greece, was advanced to the highest degree of refinement; and the sublime exclamation of Plato: “Light is truth, and God is light,” approaches nearly to a divine revelation.