the surface of the Sun; sometimes described as looking like rice-grains scattered lavishly.

But for the help given by a total eclipse, we might never have known of the red ocean of fire, or of the beautiful corona. They can now be examined, even when no eclipse is going on, by means of the spectroscope; but they were first discovered through observations at the time of an eclipse.

An eclipse of the Sun is caused—not, like an eclipse of the Moon, by the Earth passing exactly between Sun and Moon, but-by the Moon passing exactly between Sun and Earth. The little Moon, being so near to us, while the huge Sun is so far away, just suffices for a very short space to hide or nearly to hide the whole Sun. Sometimes only a part of the dark body of the Moon crosses over only a part of the bright body of the Sun; but sometimes we have what is called a Total Eclipse. Yet even then, though the dazzling face is completely veiled, the rim of crimson stands out just beyond the Moon's dark covering body; and out of that ocean of fire are seen to spring vast prominences or" flames" usually invisible to us. These prominences are clearly shown in the two illustrations.

III. SPOTS AND "FLAMES "

All that we see, commonly, when we give a glance at the Sun, is a round and dazzling face, too dazzling to be safely examined without smoked or tinted glasses. If we did carefully thus examine that surface, we might possibly catch a glimpse of one or two tiny dark spots.

p. 138

For the Sun is often spotted, and frequently with spots large enough to be made out by the naked eye. Men were very long discovering this fact, which perhaps shows how seldom they could have taken the trouble to observe with real care.

It was by means first of these spots-small as we see them, but by no means small in reality-that his turning on his axis became known. They were watched, travelling across the bright disc, taking ten or twelve days for the journey, then disappearing behind, and in about another twelve or fourteen days re-appearing on the opposite side. For though they are not permanent features, they often last for a considerable time, changing their shapes indeed to a certain extent, yet not so much that they cannot be easily recognised, even after many days of absence.

Like the "bands" of Jupiter, they are usually found only within a certain distance north or south of the equator. Whether they sink deep into the Sun's surface has been a question much discussed. The more general view now seems to be that they are, in all probability, shallow, possibly almost flat. But they are often enormous in extent. One huge specimen, seen in February 1905, was described as covering "more than four thousand millions of square miles." Our small Earth would not go far towards filling up that hollow—if it be a hollow!

Mention has been made of " sharp red heights springing from the crimson ocean of fiery gases which clothes the Sun. They are generally called "prominences," and sometimes flames or flames," as already explained.

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In size they are extraordinary, not as to flat extent, but as to height. Like spots, they may last for many days, and have even been recognised as re-appearing after absence. It is only possible for us to see them when they are on the rim—the “limb "—of the Sun, standing out against the sky. We then have a view of them sideways, instead of looking up at them from below. As the Sun incessantly turns round and round, each part of his surface in succession is at the edge. So for two or three days they become visible, standing out, and then they vanish, perhaps to re-appear later on the opposite edge.

The number seen at any one time varies. Sometimes they are very few; sometimes as many as twenty or thirty may be there. In height they differ much. More usually they range from about twenty-five to eighty thousand miles, but monster prominences are observed, very much beyond this. A French writer recently described them as "gigantic eruptions of flame, ten times, twenty times, fifty times, higher than the whole diameter of the earth." 1

Frequently the upward rush of these glowing gasmasses has been watched from Earth. And while some continue for at least a week or two, others are startlingly rapid in their growth, and short in their existence. Such outbursts, like earthly cyclones, may be either slow and lasting or rapid and soon over. But we can hardly speak in the same breath of our infantine tornadoes or whirlwinds, side by side with the tremendous eruptions on the Sun.

These Sun-flames were mentioned in a chapter on the Moon, as being so lofty that, if our Earth were as near 1 L'Astronomie, September 1919, p. 9.