limbs; but the larger have for the most part flat bottoms within, from which rises centrically a small, steep, conical hill. They offer, in short, in its highest perfection, the true volcanic character; and, in some of the principal ones, decisive marks of volcanic stratification, arising from successive deposits of ejected matter, may be clearly traced with powerful telescopes."

The appearance of these "cup-shaped" summits, or craters, will be remarked as conspicuous in my figures. The "foreshortening," mentioned above, belongs to the perspective of the circles which are turned away from the eye, upon the retiring sides of the globe or ball of the moon.

The figure upon the next page, besides showing you some of these craters of the volcanoes in the moon, shows you also the moon in its

How does Sir John Herschel's account of the numerous craters in the moon, agree with the circular figures upon Parley's three maps?

What are the craters of volcanoes?

What is the telescopic figure of the moon in its decrease?

decrease, or third quarter; or when only its

eastern half is enlightened.

CHAP. VI.

ABOUT THE VOLCANOES IN THE MOON. ABOUT THE LIKENESS OF THE VOLCANOES IN THE MOON TO THOSE UPON OUR OWN GLOBE. ABOUT CLOUDS AND WATER IN THE MOON.

THE existence, however, of volcanoes, in these mountains in the moon, was not steadily believed till they were described by Sir William Herschel.

In 1778, Don Ulloa, observing an eclipse of the sun, saw a small bright spot, like a star, near the edge of the moon; but "supposed it to be a hole or valley, which permitted the sun to shine through it."

But astronomers began at length to suspect, that the lunar appearances of this kind belonged to volcanic eruptions; and in 1787, (ten years after the observation of Don Ulloa,) Sir William Herschel published what follows: "On April

When did the existence of volcanoes in the moon begin to be believed? What did Don Ulloa observe in the year 1778?

19th, 10h. 6m. I perceived three volcanoes in the dark part of the new moon. Two of them are either extinct, or otherwise, in a state of going to break out. . . . .The third shows an actual eruption of fire or luminous matter its light is much brighter than the nucleus of the comet which M. Mechin discovered at Paris on the 10th of this month." On the night succeeding the 19th of April, Sir William found his third volcano burning with greater violence; and, by measurement, he found that the shining or burning matter must be more than three miles in diameter: it was of an irregular round figure, and very sharply defined about the edges. The two other volcanoes resembled large faint nebules, or brightish clouds or vapours, gradually brighter toward their centres, but without any well-defined luminous spots. "The appearance, adds Sir William, "of what I have called the

What discovery was made by Sir William Herschel, in the year 1787?

actual fire or eruption of a volcano, exactly resembled a small piece of burning charcoal, when it is covered by a very thin coat of white ashes, which frequently adhere to it when it has been some time ignited; and it had a degree of brightness about as strong as that with which a coal would be seen to glow in a fair daylight."

The same appearances in the moon had actually been observed at the Royal Observatory at Paris six days before their being seen by Sir William Herschel; and described as like a star of the sixth magnitude, but with a brightness occasionally increased by flashes.

Other French astronomers saw the same thing; as in the example of M. Villeneuve, on the 22d of May, 1787. The volcano referred to is on the north-east part of the moon, about three degrees from its edge, and toward the spot which astronomers call Helicon.

But, here, from the names Apennines, Heli

Were Sir William's observations, concerning the existence of volcanoes in the moon, confirmed by those of other astronomers?