STUDY VIII. DAY I.-LIGHT. "Truth is the Body of God, and Light is His Shadow."-PLATO. STELLAR Worlds existed before the earth. The poetry of Job (xxxviii. 7) is beautiful and true: when the foundations of the earth were laid, "the morning stars sang together, and all the sons of God shouted for joy." We adopt the words of St Jerome "What eternities, what times, what originals of ages, must we not think there were before; in which angels, thrones, dominions, and the other powers served God; and existed apart from the changes and measures of times?" "God said "Let there be light :' And forthwith light Ethereal, first of things, quintessence pure, Light had shone long before in Heaven, and ancient stars had ere this been kindled. We believe this, though no scientific proof, so far as we know, exists that any fixed star or nebula is older than our sun. "Let light be," is the command. "There was light," is the substitution, on earth, of light for darkness. Light is a wave-like movement, a peculiar shivering motion, of the ultimate particles of bodies. The all-pervading æther takes up these molecular tremors, and conveys them with inconceivable swiftness to our organs of vision. This transported shiver of bodies, millions of miles distant, which awakes the splendour of day, and shines in the firmament at night, is, when translated into human consciousness, light. When we detect by a thermometer, or by the sensation that from which, as Locke says, we denominate the object "hot," that is heat; and when we become aware of it by the eye, it is called "light." "There Our Conception of Light. 143 is no body in nature absolutely cold," says Professor Tyndall, "and every body not absolutely cold emits rays of heat." To render radiant heat visible, it must be raised to a certain temperature, when it emits a feeble red light; as heat grows, light augments in brilliancy, until, finally, it is dazzling white. "The difference between radiant heat and light is simply the difference between a low note and a high one.' If we conceive the universe as consisting of non-luminous, formless matter, and then, in scientific use of imagination, endeavour to realise the growing warmth of all things, as the vibrations of matter are quickened and intensified into the amplitude of luminous oscillations in the various series of worlds, we shall have some faint conception of God's wonderful work when He said "Let there be light." "Yet the sun Was not, she in cloudy tabernacle "Ignea convexi vis et sine pondere cœli Emicuit, summaque locum sibi legit in arce." OVID, Met. Lib. i. "Fire rose out of the formless mass, hung like a curtain on the roof, as it were, of the world; making light in the vaulted sky, and clothing it with a luminous vapour light." Or, more scientifically, "As in nebulous sphere, just become luminous, and in the new red hot liquid earth of our modern cosmogony, light was not yet divided into suns and stars, nor time into day and night." Let a current of electricity, of gradually increasing strength, be sent through a platinum wire; the particles of metal instantly vibrate with accelerating speed, and the wire becomes warm to the touch; but there is no light. At length, when the heat has grown, there is a faint red illumination. The glow augments with increasing heat, the red becomes more brilliant, orange rays are added; besides these appear yellow, then the green come, and in succession, blue, indigo, and violet rays. When the wire is white-hot, the simultaneous action of all the colours produces the effect or 1 "Recent Advances in Physical Science: " Professor P. G. Tait. impression of whiteness on the optic nerve, and the light is perfect or white. We now, in some measure, have a conception of light going forth out of darkness. At whatever period, or in whatever manner, during the integration of our solar nebula into a planetary system, light began to shine, the heat would be the equivalent of the work of integration; and as the heat quickened in vibration, from the low to the high note, the brightness would increase the energy of heat would be transformed more or less into that of light. If the whole mass of the earth was agglomerated almost at once, and if the different rent parts impinged together with properly arranged velocities, we can note the state of things before and after that moment. Before were scattered masses of matter. Then, at the instant of impact, the integrated mass became of high temperature and light shone. Before that moment was darkness, after it was light. We cannot imagine that Moses, though learned in the wisdom of the Egyptians, knew this; or that the elementary atoms have their own shapes and powers, whereby they arrange themselves into molecules of exceeding complication and varying vibration; or could be aware that 458,000,000,000,000 vibrations in a second are necessary, in order to give us the consciousness of the lowest or red light; and we wonder that, in relating the primal illumination of the earth, he tells us first of the light, and after that of the luminous body-the sun. With higher reverence than any regard for his own wisdom draws forth, we meditate on the words "The earth was without form and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters. And God said, Let there be light: and there was light." That which caused the integration of the earth, and the production of light and heat, was energy. Energy may be defined as the power of doing work. There is always a tendency, in every transformation of energy, to pass from a higher to a lower form; indeed, all the energy in the universe is passing on to the lowest and final form of equally diffused heat. This, the dissipation of energy, is by no means well understood. There can be little question that the principle concerns the whole theory of thermo-electricity, of chemical combination, of allotropy, of fluorescence, &c., and perhaps matters of a higher order than common physics and chemistry. In astronomy, it shows us the material of potential suns, suns in the process of formation, in vigorous youth, in the phase of habitation for life, and in every stage of lingering decay. It reveals to us every planet and satellite as formerly a tiny sun. It carries forward our thought to that time when the materials of present systems shall be component parts of future larger suns and planets. Finally, it conducts us to that necessary future, if physical laws remain unchanged, when the present warm glittering show of life will be dark and cold and dead. It also reminds us of a beginning, a state beyond which we are totally unable to penetrate, a state produced by other than now visibly acting causes, by that transfer of energy from the Unknown, of which the universe and all material phenomena are memorials. The elementary atoms, possessing their own shapes and powers, arrange themselves into molecules of manifold combination, and exceeding variety of vibrations. When raised to incandescence, or white-heat, and their lights are tested by spectrum analysis, the glowing vapours indicate, by luminous lines, the different elements which are in combustion: thus we are learning of what materials the sun and stars are composed. Heat and light are the product of a transfer of energy. Transfer of energy, through a solid body, is effected simply by vibration of the solid body; through air, by setting it in motion at its own period of vibration; through what we call a vacuum, by the magnetic medium-that which Clerk-Maxwell gives reason to believe is the medium which conveys light and radiant heat. Vibrations, occurring less frequently than sixteen times in a second, produce in us consciousness of a succession of noises. Vibrations occurring oftener than 16, but less than 30,000 times in a second, produce in us the consciousness of musical notes, varying in pitch with the vibrations. Vibrations occurring oftener than 30,000, but less than 458,000,000,000,000 times in a second, do not K affect us through the ears; but the more rapid ones, acting through the nerves of the skin, produce in us the consciousness of heat. Vibrations at the rate of 458,000,000,000,000 in a second, affect us through the eyes, and produce our consciousness of red light. As the vibrations increase, corresponding shades of colour appear, until, at the rate of 727,000,000,000,000 in a second, we have the consciousness of violet light. Higher rates produce no definite state of consciousness in us. Thus, by one and the same external agency-vibrations among particles of matter—are sensations caused different, as sound, heat, light. In sound-waves, the particles of air vibrate back and forward in the direction travelled by the sound. If, by another sound, we raise such undulations as fill the depressions in the waves of the former sound, this adding of sound to sound will cause silence. Light and heat travel at the rate of about 186,000 miles a second, the direction of the vibrations is across the direction in which they move, two sets of rays may be made so to interfere with one another, as to be mutually destructive: the two rays of light produce darkness, and the two rays of heat cause heat to disappear.1 Passing a slice of solar or of electric light through a prism, we unroll it into the beautiful colours of the spectrum. At one end is the red, at the other the violet, the remaining prismatic colours lying between. Red is hottest of the colours, and beyond it are the invisible rays called heat rays. Violet is the coldest, and beyond it are the actinic or chemical rays, also invisible. In the three, heat, light, actinism, reside the miraculous generative energy, which fills the earth with warmth, life, and splendour. Concerning their nature, whether we call it vibration, or heat, or light, or actinism, we affirm nothing, and know nothing. Aristotle, one of the most thoughtful men, would say the energy streamed from God, the Infinite and Eternal Mind, as light issues from the sun. To a certain extent, we can give a mechanical explanation of heat and light, as the products presented to our consciousness of a perpetual trembling, or swaying to and fro, of the invisible atoms of which visible bodies are composed; but, 1 "Recent Advances in Physical Science," p. 205: Professor P. G. Tait. |