What causes are supposed to produce these spots ?

Some philosophers have been of opinion, that they are occasioned by the smoke, and opaque matter, thrown out by volcanoes, or burning mountains of immense magnitude; and that, when the eruption is nearly ended, and the smoke dissipated, the flames are exposed, and assume the appearance of luminous spots. Others have supposed them to be occasioned by a number of planets, circulating round the sun, at a small distance from its surface; and others, that they are clouds, floating near its surface. The opinions of M. de la Hire, Dr. Alexander Wilson, Mr. King, and Sir William Herschel, are interesting.

What was the opinion of M. de la Hire?

The sun he imagined to be in a continual state of fusion, and that the spots, which we observe, are only the eminences of large masses. of opaque matter, which by the irregular agitation of the fluid, sometimes swim upon the surface, and at other times sink, and disappear.

What has Dr. Alexander Wilson, of Glasgow, attempted to prove?

That these spots are excavations in the lu minous matter, that environs the sun's body, and which is probably of no great depth.

What were Mr. King's sentiments?

In 1788, this gentleman published a disser

tation on the sun, in which he advanced the opinion, that the real body of the sun is less than its apparent diameter; that we never discern the real body of the sun, except when we see its spots; that the sun is inhabited as well as the earth, and is not necessarily subject to burning heat; and that there is in reality no violent elementary heat essentially existing in the rays of the sun themselves, but that they produce heat only, when they come in contact with the planetary bodies.

But what is the opinion of Sir William Herschel?

He supposes the solar spots to be the opaque ground or body of the sun, and that the luminous part is an atmosphere, which being intercepted, or broken, gives us a view of the sun himself.

Do the ancients appear to have had any notion of these spots in the sun?

They generally consider it to be a body of pure fire.

Will you tell me, my dear mamma, how you understand the account given of the creation of the sun in the book of Genesis. I read, God said on the first day, "Let there be light, and there was light'" and on the fourth day, "God said, Let there be light in the firmament of the heaven, to divide the day from the night."

It appears probable, that the particles of

which the sun is composed were the first day's work, and that the concentration of them into one body, was the work of the fourth day.

There is a very interesting fact, which was first observed by Mr. Childrey, about the year 1650, with which I should wish you to be acquainted.

What is that?

It is what is termed the zodiacal light, first so called by Cassini, in 1683, and by him described in the following manner : "This light accompanies the sun, and is usually attributed to his atmosphere. It is seen at some seasons of the year, either a little after sunset, or a little before sunrise. It appears at first sight like a faint, whitish zone of light, resembling the milky way. Its borders are then ill defined, and scarcely to be distinguished from the twilight, which is seen commencing near the horizon. As it ascends above the horizon, it becomes brighter, and larger, to a certain point, after which the approach of day renders it gradually less apparent, till it becomes quite invisible. The direction of its longer apparent axis, is observed to be in the plane of the sun's equator, but its length is subject to great variation, so that the distance of its summit from the sun varies from 45° to 120°."

CHAPTER VI.

OF THE FIGURE AND MOTION OF THE EARTH.

Of the general questions, which respect the earth, some must be allowed to occupy their appropriate places among the rest of the planets; but I wish now to direct your attention to two topics, respecting the earth, namely, its figure and motion.

In a former lecture, mamma, you told me, that Anaximander asserted that the form of the earth was cylindrical. Who was it that discovered the earth to be spherical ?

It is not known, but the doctrine is of great antiquity.

Will you show me, that the doctrine is of great antiquity?

At the taking of Babylon by Alexander the Great, eclipses were found to have been set down, and computed for many centuries, which, without a knowledge of the globular figure of the earth, could not have been known.

Can you give me another instance ?

Thales, the Milesian, who lived about six hundred years before Christ, was acquainted with this fact.

But though this fact was known to some

philosophers, are there not many proofs, that this knowledge was confined to a very few persons?

Yes; some of the greatest poets, and mathematicians, were ignorant of it. Heraclitus, a Greek philosopher, who lived about five hundred years before Christ, thought the earth was in the form of a canoe.

What did Aristotle think?

That it was in the form of a timbrel.

And what was the opinion entertained by most persons respecting the figure of the earth? It was supposed to be a large circular plane. But what really is the form of the earth? The earth is of a round or spherical figure, nearly resembling a globe.

Will you mention to me one evidence of the earth being a round body?

The voyages of Sir Francis Drake, Lord Anson, and Cook, who set out at different times, and by steering almost continually westward, arrived at the places from whence they departed.

Can you give me another proof or two?

The circular appearance of the earth itself, and the loss of the view of the lower part of a vessel, before the upper part disappears; which must arise from the water between the beholder and the vessel, having the form of a curve. The circular shadow of the earth upon the face of the moon, in the time of a lunar eclipse, evinces