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advancing but invisible earth. When the latter had nearly covered the sun, its whole outline would be shown to him by a red light surrounding it, caused by the refraction of the earth's atmosphere. Finally, when the last trace of true sunlight had disappeared, nothing would be visible but this ring of bright red light having inside of it the black but otherwise invisible body of the earth.

The circumstances of an eclipse of the moon are quite different from those of a solar eclipse, to be described in the next chapter. It can aways be seen at the same instant over the whole hemisphere of the earth on which the moon is shining at the time. A curious phenomenon occurs when the moon rises totally eclipsed. Then we may see it on one horizon, say the eastern one, while the sun is still visible on the western horizon. The explanation of this seeming paradox is that both bodies are really below the horizon, but are so elevated by refraction that we can see them at the same time.