Of course, the same result of heat and light would follow from compression, if a body had the power of contraction in itself.  We endowed every particle of our gas, myriads of miles in extent, with an attraction for every other particle.  It immediately compressed itself into a light-giving body, which flamed out through the interstellar spaces, flushing all the celestial regions with exuberant light.

But heat exerts a repellent force among particles, and soon an equilibrium is reached, for there comes a time when the contracting body can contract no farther.  But heat and light radiate away into cold space, then contraction goes on evolving more light, and so the suns flame on through the millions of years unquenched.  It is estimated that the contraction of our sun, from filling immensity of space to its present size, could not afford heat enough to last more than 18,000,000 years, and that its contraction from its present density (that of a swamp) to such rock as that of which our earth is composed, could supply heat enough for 17,000,000 years longer.  But the far-seeing mind of man knows a time must come when the present force of attraction [Page 21] shall have produced all the heat it can, and a new force of attraction must be added, or the sun itself will become cold as a cinder, dead as a burned-out char.

Since light and heat are the product of such enormous cosmic forces, they must partake of their nature, and be force.  So they are.  The sun has long arms, and they are full of unconquerable strength ninety-two millions, or any other number of millions, of miles away.  All this light and heat comes through space that is 200 deg. below zero, through utter darkness, and appears only on the earth.  So the gas is darkness in the underground pipes, but light at the burner.  So the electric power is unfelt by the cable in the bosom of the deep, but is expressive of thought and feeling at the end.  Having found the cause of light, we will commence a study of its qualities and powers.

Light is the astronomer’s necessity.  When the sublime word was uttered, “Let there be light!” the study of astronomy was made possible.  Man can gather but little of it with his eye; so he takes a lens twenty-six inches in diameter, and bends all the light that passes through it to a focus, then magnifies the image and takes it into his eye.  Or he takes a mirror, six feet in diameter, so hollowed in the middle as to reflect all the rays falling upon it to one point, and makes this larger eye fill his own with light.  By this larger light-gathering he discerns things for which the light falling on his pupil one-fifth of an inch in diameter would not be sufficient.  We never have seen any sun or stars; we have only seen the light that left them fifty minutes or years ago, more or less.  Light is the aerial sprite that carries our measuring-rods across the infinite [Page 22] spaces; light spreads out the history of that far-off beginning; brings us the measure of