in the preceding lecture. Chaos means confusion. The nebula was but a subtle vapor. As yet nothing had assumed definite form or character. There was the germ of worlds, but no world. There were the elements of water and air and light, while as yet there were none of these, none of the chemical combinations or mechanical unions so familiar to us now; and the various changes in nature that we know so well to-day, had not begun. There was absolutely nothing but the dark chaotic deep. But while it is possible to conceive of the original nebula as dark-for dark as well as luminous nebulæ still exist-we cannot suppose it continued long in absolute darkness, for one of the first effects of chemical action would be the production of light, though that light might be long obscured by overlying vapors. We need not concern ourselves here with the nature of light-whether, according to the older physicists it is luminous matter radiated with immense velocity from the light-giving body or centre, or according to the more recent and probable theory that it is merely the undulations of a universally diffused ether. Either theory will answer our present purpose.

Nature of

Light.

Cosmic and

Solar Light

For the sake of convenience in this discussion we shall speak of light as of two kinds, cosmic and solar; the first produced by chemical action in the nebula itself, the

other coming from the sun. This use of the term, “cosmic" may be open to criticism, but we use it for want of a better, meaning by it just what is stated, light caused by the nebula of the earth itself, after it was thrown off from the greater mass. It may, therefore, be called earth light or world light. While by solar light is meant that proceeding from the sun.

And now, going back to the point at which we left the incipient earth in the former lecture, let us carefully observe what changes came about. We deal now with the earth nebula, leaving for the time, all the others out of the account.

There is a dark nebulous mass, some two thousand times as great in diameter as the present earth, floating or wheeling its ample bulk through space.

The earth a nebula.

The nebula changing.

But as steam does not remain steam long after exposure to the air, but changes to a denser form occupying so much less space, so this vast vaporous body had not proceeded far in its course till the outer portions began to condense, or change toward a liquid and then a solid form, by which operation, of course, the mass was being continually reduced in size. The heavier particles gradually gathered toward the centre, forming the nucleus possibly of a solid globe, while the greater part still remained,

a sort of cloudy envelop about it. But while the steam from the locomotive may change to a mist that we feel upon the face, or fall like scattered rain-drops on the ground, leaving their imprint in the dust, this nebula contains not merely water reduced to steam, but all the elements of all the material that now enter into rock and soil, in the form of a finely attenuated gas or vapor; and these are undergoing a change from their present to a more stable condition. The minute atoms of iron are uniting, forming larger particles; the atoms of lime are combining, and so on through a long list. And as this process goes on a glow comes over the mass like the first faint dawnings

of the day. The surface of the body is at white heat, and it gives forth a dim light.

The earth

lighting up.

But as the process still goes on, the gathered particles change to a clear red color. The surface is now red-hot, and lights up all the space around, and the earth has the appearance of a blazing star. To state it more concisely, the earth nebula is a blazing star.

This is what we have called cosmic light-not coming from the sun, but produced by the earth itself as it hung like a brilliant meteor in the sky. Something analagous to this may be easily witnessed.

Analogy of heated iron.

Go into a blacksmith's shop, and heat a piece of iron as highly as can be done with a common bellows. It comes from the fire, of a whitish color, emitting an indistinct glow, not unlike the aurora or the dawn. Wait a moment, and at a different temperature it changes to red. It is red-hot, and will cast a glow of light far out into the night. Such was the change through which the earth nebula passed, from a dark, chaotic state, till it became a luminous body, shining with its own light. And it was by such. means the fiat, "Let there be light,” was first answered and obeyed.

But now comes another important change.

To extend the foregoing illustration: if you observe the iron in the forge, from the brilliant and luminous condition of red

The earth becomes

opaque. heat, it soon changes to a dark color and becomes opaque, showing no light at all, any more than if it were cold iron, though it may still be somewhat hot. A similar change passed upon the earth; not immediately, for the larger the body the longer the time required in process of time the earth became dark again; for it had so far cooled, and the matter had so far condensed, that a thin crust had formed all around , on the same principle that a slag will form on of melted metal, though the interior may

cooling. But in

remain a long time after in a heated and even molten condition. A bed of fresh volcanic lava, also, will retain a perceptible degree of warmth for many years, varying according to its thickness. and other modifying circumstances.

The process

reviewed.

Thus we trace the series of changes through which the earth passed; from, first, a vast ball of vapor to a body of liquid or molten substance-emitting first the glow of white heat and then the light of red heat-and thence to a globe having a thin crust upon it, and so beginning to assume somewhat the appearance and character of the modern earth. As the process continued and the cooling went on, of course the crust grew thicker by degrees and more substantial, and thus was it fitted at length for the production and maintenance of life in its various forms.

We are not yet prepared, however, to follow the earth in its development of soils and seas and rocks and rivers, for there are other matters that must be considered before we can present an intelligible view of the creation as a whole.

We have to do in this chapter especially with Light. We have spoken of light as of Distinctions two kinds, and it is important that we

of cosmic

and solar

light.

keep in mind the distinction between the two. That already described as Cosmic Light, not