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about going down into the Earth and out on the further side, in any such fashion, we are talking about an unknown region. The outside surface of our globe is more or less familiar; but not the inside.

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A recent statement gives as the greatest depth of a mine ever yet sunk: "the No. 3 shaft of the Tamarack mine in the county Michigan," which "reached vertical depth of about 5200 feet; " that is, slightly under one mile. A mere scratching of Earth's crust! Even if we suggest a larger margin, and say that no mine has reached a depth beyond two miles-what are two miles compared with eight thousand? True, parts of our ocean-bottoms lie six or even seven miles below the ocean-surface; but those depths are far beyond our reach.

Imagine what it would mean to delve four thousand miles below the surface of our Earth; four thousand miles away from light and air; nearly four thousand miles beneath our oceans. And to complicate matters, the inside of our world is believed to be intensely heated; so much so, according to one authority, that about thirty miles down the heat must be great enough to melt all solid rocks. If they are not there in an actually molten state, it is only because the immense pressure tends to keep them solid.

Such a road would indeed utterly dwarf the grandest engineering works of man.

Though a road of this kind is impossible, and though we cannot hope ever to dig or blast our way downwards until the opposite side is reached, yet the actual size of our Earth has been again and again reckoned. The size of any globe, both through the middle and round

the outside, may always be found out from careful measurements of parts of its surface. The work of surveyors comes in here; and such measurements have been made times without number, and calculations worked out therefrom.

We now know, as a matter of certainty, that the Earth is about eight thousand miles through from pole to pole or from side to side straight through the centre, and about twenty-five thousand miles round at the equator.

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By the "equator we mean an imaginary line round the Earth, half-way between the north and south poles. And when we speak of the north pole or the south pole in the heavens, we mean always that point in the sky which lies just over our Earth's north pole or our Earth's south pole.

With regard to the shape of our Earth, it is, as already stated, a globe or ball; more strictly, it is like an orange, since it has slightly flattened poles. In scientific language the Earth is an "oblate spheroid; oblate spheroid;” and in connection with this term a little scene of past days comes to mind.

My father one day was showing cube-shapes to two little girls, aged about nine and seven, explaining their names and uses. In a corner of the room their small sister, only three and a half or possibly as much as four years old, was seated on the floor, playing happily with her toys.

Presently, to see how far his explanations had been understood, my father asked a question or two, and among them: "What is the shape of our Earth?"

Seven-years-old and nine-years-old tried to remember. But the baby in the corner, busied with her dolls, had listened to some purpose, and the pause was broken by a sweet little treble voice piping out"An oblate spheroid, uncle!

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My father's surprise and amusement may well be imagined.

And perhaps I cannot do better than mention here how deep is my debt to that dear father for his early lessons in science; lessons which familiarised me as a child with scientific modes of thought and expression; laying a firm foundation, upon which a superstructure of further study could so easily be reared. It was he who first awoke my interest in such subjects; he who made Astronomy a living force in my imagination.

The teaching must have begun very early, for I well remember standing by his side, one wintry day, when I was certainly not more than seven or eight years old, asking why and how it could be that we were nearer to the Sun in winter than in summer, and yet were more cold. A fire was burning, and he sat not far off. I can see now his fine, stately figure, the short-frocked child standing by his side, and the gesture with which he pointed to a fly on his knee. "See if that fly were one inch nearer to the fire, would it feel any hotter?

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No; it would not. I understood that instantly; and though the real cause of summer and winter in the slant of Earth's axis did not become evident till long after, I did see then, with daylight clearness, that the difference of three millions of miles, compared with the Sun's whole distance, was no more than that one inch in the fly's

distance from the fire. There was

no need to ask

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Heaven's ebon vault,

Studded with stars unutterably bright,

Thro' which the moon's unclouded grandeur rolls,
Seems like a canopy which love has spread
To curtain her sleeping world."

P. B SHELLEY.

PART II

STUDYING THE HEAVENS

I. GROUPS OF STARS

LIKE every study, that of Astronomy has to be from small beginnings. To start with a difficult text-book, or with hard calculations, would in most cases have no good result.

It is a study which ought to be followed on two lines at the same time. Much can be learnt from books; much also from actual observation of the sky. A beginner may choose the one plan or the other; but the better mode is to use both plans.

Without books, a student of the skies stands in much the same position as an ancient astronomer of Chaldean days. He has to find out for himself those things which have taxed the minds of men through centuries. And without some amount of watching of the heavens, the known facts which may be learnt from books can never be quite so real to him, if he does not use his own eyes to verify them, to the small extent which lies in his power.

Some teachers of Astronomy prefer to start with the distant stars, and to work their way back to such heavenly bodies as lie nearer to Earth. Others think it wise to tackle first the nearer bodies, and gradually to wander

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