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centre of the sun; yet the moon may not be in such a situation as to allow it to hide from us the whole surface of the sun, or its twelve digits. In that case, so much of the sun's disc as is not eclipsed will be seen to surround the moon annularly, or in the manner of a ring; and how this variation happens, I am going to explain.

If your brother's hat is held before his eyes in a situation very near to his face, that small hat will be sufficient to hide or eclipse from him a great castle. This, then, is a central and total eclipse.

If it is held a little further off, but still straight before his eyes, it will no longer hide or eclipse the whole of the castle; for a part of the castle will appear round the whole circle of his hat. This, then, is a central and annular eclipse.

Thus, it is no change of size in the moon, any more than in the hat, which causes the change of its capacity totally to hide or eclipse the sun; but only the change of its place, or the

degree in which it is near or distant from the earth, at the time of its passing between the earth and the sun.

But, further, there is always a possibility, both of an annular eclipse, and of a total eclipse which is not central.

My figure, at two pages back,r epresents the central and annular eclipse of the 15th of May, 1836; but that eclipse was thus seen only in a small part of the British Islands, and of some other countries. The figure shows the moon not yet arrived exactly in the centre of the sun. The small black lines which appeared to connect, for a moment, the right edge of the moon with the right edge of the sun, were optical illusions.

Over leaf you will see a clever and goodnatured little boy, who, having smoked a piece of glass against the time of the eclipse, that himself and his smaller sister might have a nice view of it when it came, is now holding it before the one eye which she keeps open, both to enable her

to see, and to prove that his

glass has been For you must

For

smoked just as it ought to be. know that his sister is a little awkward in using it; and has two or three times dazzled her eyes sadly, by looking on one side of it, instead of through it!

By the side of my infant astronomers is a tame raven, which, rather more affected than they by the sun's dimness, but less curious as to the particulars, has put his bill under his wing, to take a nap.

[graphic]

CHAP. XXV.

WHY THE SUN AND MOON APPEAR LARGER WHEN ON OR NEAR THE HORIZON, OR AT THEIR RISING AND SETTING, THAN WHEN IN THE ZENITH, OR IN THE MIDDLE OF THEIR COURSES.

You expect me to tell you how it happens, that the sun and moon, as seen in different parts of the heavens, appear to vary in their sizes. I am glad to know that you pay attention to these changes in natural appearances, and give your minds to understanding their causes; but these apparent changes of magnitude of the sun and moon, it seems to be much thought, do not admit of scientific explanation, and have no cause but in our modes of judging of the magnitude of bodies with our eyes, according as those

Do the sun and moon appear to vary in their sizes, according as they are nearer or further off from the horizon or the zenith?

bodies have or have not any other bodies near them, by the help of which we can form comparisons.

Your question, in the meantime, is one which is often asked by persons much older, and more wise, than yourselves. Eminent philosophers, astronomers, and mathematicians have proposed several and very different explanations.

sons,

I have no doubt but that you, like other perhave been inclined to fancy, that the sun or moon, when on or near the horizon (that is, when they really seem nearer to the earth, or to the landscape,) appears larger to you than when they are in the middle sky, precisely because they are actually nearer to you; just as your dog, or your horse, or a ship, or a coach, or a balloon, seem larger when they are near you, than when they are further off.

What is the horizon?

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