Scientific American 10, 6.3.1869
MESSRS. EDITORS: — Rays of light, however brilliant they may be, are invisible when they pass through a dark room, or any other dark place, unless they are arrested, held, and refracted by some substantial thing. Now, the space intervening between the earth and the sun, and all other spheres, is an absolute void, excepting the distance reached by the earth's atmosphere. Through this immense space, and through all space not occupied by matter, the sun penetrates with its bright rays; yet, utter darkness - intense blackness - occupies and prevails in all this void, because there is no matter or thing therein to arrest, hold, and refract rays of light. Were it possible that one could be placed at a point midway between the earth and the sun, nothing could be seen other than spark-like spheres bedecking a black firmament in all directions. All these, even the sun, would appear only as bright balls of light, with or without radiation, just as light appears to the mariner through the darkness of night. The appearance of this darkness - this blackness, is modified to our sight here by the halo caused by refracted light from objects immediately surrounding us on the surface of the earth and from vapors in the earth's atmosphere; and it is this mod-ified blackness which causes the apparent blue color of the skies.
-Richard A. Whitmore
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