The first attentive observer of the sun, Scheiner, at first regarded the spots as satellites--an indefensible opinion, which, however, some have attempted to revive. Galileo attributed them to clouds or vapors floating in the solar atmosphere; this was the best conclusion which could be drawn from the observations of that epoch. This opinion met for a long time with general approval; it has even been renewed in our day. Some astronomers, and among them Lalande, believed, on the contrary, that they were mountains, of which the flanks, more or less steep, might produce the aspect of the penumbra--an opinion irreconcilable with the proper motion which the spots sometimes possess in a very marked manner. It is not usual, in fact, to see mountains traveling. Derham attributed them to the smoke issuing from the volcanic craters of the sun, an opinion revived and maintained in recent times by Chacornac. Several _savants_, regarding the sun as a liquid and incandescent mass, have also explained the spots by immense cinders floating on this ocean of fire. But a century had scarcely elapsed after the epoch when the spots were observed for the first time, when an English astronomer, Wilson, showed with certainty that the spots are hollow. We do not know with any certainty whether the sun is through and through one mass of glowing molten heat, or whether he may have a solid and even cool body within the blazing covering. Some have thought the one, and some the other. We only know that he is a mighty furnace of heat and flame, beyond anything that we can possibly imagine on our quiet little earth. It seems very sure that no such thing as “quietness” is to be found on the surface of the sun. The wildest and fiercest turmoil of rushing wind and roaring flame there prevails. The cyclones or hurricanes which take place are sometimes so rapid and so tremendous in extent, tearing open the blazing envelope of the sun, and showing glimpses of fiery though darker depths below, that we, on our far-distant earth, can actually watch their progress. Astronomers speak of the “quivering fringe of fire” all around the edge of the sun, visible through telescopes. But the sun is perpetually turning on his axis, so that each hour fresh portions of his surface thus pass the edge, showing the same appearance. What conclusion can we come to but that the whole enormous surface of the sun is one restless, billowy sea of fire and flame? It sounds to us both grand and startling to hear of the mighty outbreaks from Mount Vesuvius, or to read of glowing lava from a volcano in Hawaii pouring in one unbroken stream for miles.