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:"

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 comes, and in succession, blue, indigo, violet rays. When the simultaneous action of all the colours produces the effect or impression of whiteness on the optic nerve, they are blended into one, and the light is perfect.

We now, in some measure, have a conception of light going forth out of darkness. At whatever period, or in whatever manner, during the formation of our solar nebula into a planetary system, light began to shine, the heat would be the equivalent of the work; 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,

1 "Interaction of Natural Forces: " Prof. Helmholtz.

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more or less, into that of light. If the whole mass of the earth was agglomerated almost at once, and if the different 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 knew 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 about 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.

That which caused integration of the earth, of the sun, and 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. The dissipation of energy is not fully understood. There can be little question that the principle concerns the whole theory of thermo-electricity, of chemical combination, of allotropy, of fluorescence, etc., and matters of a higher order than 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 the stages of lingering decay. It reveals 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 future, if physical laws remain unchanged, when the present warm glittering show of life will be dark and cold and dead. It also declares a beginning, a state beyond which we are unable to penetrate, 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, were arranged into molecules of various structure and variety of vibrations. When raised to incandescence, or white heat, and their lights are tested by spectrum analysis, the glowing vapours indicate, by lines, the different elements which are present: thus we learn 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 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, or ether, by the magnetic medium-which Clerk Maxwell gives reason to believe conveys light and radiant heat. Vibrations in the atmosphere, 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 the consciousness of musical notes, varying in pitch with the vibrations. Vibrations in the ether, occurring oftener than 30,000, but less than about 458,000,000,000,000 times in a second, do not affect us through the ears; but through the nerves of the skin, produce consciousness of heat. Vibrations at the rate of about 458,000,000,000,000 in a second, affect us through the eyes, and we are conscious of red light. As the vibrations increase, corresponding shades of colour appear, until at the rate of say some 727,000,000,000,000 in a second, we have violet light. Higher rates produce the invisible rays. By one and the same external agency-vibrations among particles of matter --are sensations caused-different, as sound, heat, light, and whatever belongs to the invisible rays.

In sound-waves, the particles of air vibrate back and forward in the direction travelled by 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 causes silence. Light and heat travel through ether at the rate of some 186,000 miles a second, the direction of the vibrations being across the path in which they move. Two sets of rays may be made so to interfere with one another, as to produce darkness, and the two rays of heat cause heat to disappear.1

1 "Recent Advances in Physical Science," p. 205: Prof. P. G. Tait,

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, beyond it are the invisible heat rays. Violet is the coldest, and beyond it are the invisible actinic or chemical rays. In the three-heat, light, actinism, resides the generative energy which fills the earth with warmth, life, splendour; which splits up substances and determines their combination; and some substances have power to make invisible light visible. Concerning their essence, 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-whereby the blood heats, the blossom blows, the sea rolls, the world is warmed.

To a certain extent, we can give a mechanical explanation of heat and light as the products presented to our consciousness by a perpetual trembling, or swaying to and fro, of the invisible atoms of visible bodies; but the explanation connected with the linked purpose of the whole exceeds our thought. When we contemplate the heavens some clear autumnal evening, and marvel at the beauty of Sirius, that starry splendour is brought to us by medium of atomic shivers maintained, during the past twenty-two years, at the average rate of some six hundred millions of millions of vibrations the second; and reveals a scheme of worlds and possible sphere of life, vaster than our own. Nor is that all several optical phenomena indicate that a disturbance partaking of the nature of compression would be transmitted with a speed vastly greater than the velocity of light. We may ascend by this thought to the possible nature of the means by which intelligence is conveyed to other beings of the things done in our world.

The medium used, ether, is specially fitted for the transmission of the waves which constitute light. These waves are so small, that from forty to fifty thousand are required to occupy the breadth of an inch, and trillions enter the eye during a few seconds. The red wave has a length the 10.000.000th part of an inch. In one second about 458 millions of millions of vibrations occur. At the line H, in

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the violet, the length of the wave is the Tooth part of an inch; and the number of vibrations is some 727 millions of millions the second.1 The optic nerve is not conscious of heat in the hot rays, nor of waves larger than the red, nor of those smaller than the violet. The eye sees only different proportions of the three primaries—red, green, blue; therefore, our sight may be fairly considered as rudimentary. "Take the number of fibres in the optic nerves as two hundred and fifty thousand. Every one of these is capable of innumerable different degrees of sensation of one, two, or three primary colours." 2 What a manifold undeveloped system of signs and images we have within us! We cannot but think that their wonderful potentialities prophesy of a coming richness and fulness.

In all creatures the eye is a wonderful instrument; but, probably, the eyes of insects excite highest admiration. On the heads of beetles, bees, flies, butterflies, and other insects, are two protuberances; these, examined by the microscope, are found to contain a prodigious number of small transparent hemispheres, placed with the utmost regularity in lines crossing one another as lattice-work. These hemispheres are eyes which, like so many mirrors, reflect the images of surrounding objects. Some insects possess thousands so abundant is their supply of light and gladness. An infinite adaptation of means is unfolded for our contemplation.

We know what a language of twenty-six letters does in collecting, preserving, verifying, the experiences of millions of men in thousands of generations. It seems nothing in comparison with the revelations of light from star-depths, which even our present optic nerves, when all developed into use, may translate into human consciousness, forming distinct images of operations wrought by ministers of flame, by guardian spirits, by cherubim and seraphim. We may be able to see waves of radiance, at the rate of six hundred millions of millions the second, impart their motor energy to the atoms which vibrate in unison in the molecules of growing grass and flower, and behold how these are arranged by tremulous chemical energy into their substance Spectrum Analysis," p. 11: Henry E. Roscoe. 2 "The Perception of Sight:" Prof. Helmholtz.

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