“James, my boy,” said Mr. Marple “do you know why there should be
winter and summer?
No, father, I really cannot tell. I know that in England the sun was
higher up in the day, and that he stopped up longer in summer than in
winter. But then as I believed that the sun ran about as he liked,
I was not surprised at his change of place. Now, however, I am very
anxious to know more about this subject.
When were we in the circle of the Pleiades, that is, the place where at
some time or other of the twenty-four hours they would be overhead?
O, that was long before we got to the equator.
Yes, it was about 1500 miles to the north of us. Now we are in the
circle of the Virgin cluster.
But the Bull and the Virgin belong to the twelve constellations, of
which we were talking, forming a broad circle, along which the sun
appears to travel.
True. But they are not in an upright circle. Their line will cross our
equator Line.
If that be it, the sun does not appear, then, to go round us over the
equator.
No; for if it did, it would be seen overhead at that place every day at
twelve o’clock; whereas it shifts its course continually. One day it is
over one part at noon, and upon another day over another part.
Why, if the circle of the Zodiac be inclined to the circle of the
equator, it will cross it in two places. I suppose that is the reason
why, on the celestial globe, one constellation, as the Virgin, is over
the equator circle; others, as the Bull, over some place to the north
of it; and some others, as the Scorpion, to the south.
You guess rightly.
Then if that be it, the sun must appear to cross the equator twice in
the year.
It does so on the 21st of March and 23rd September. These are the
vernal or spring equinox, and the autumnal equinox. March is the
vernal equinox of London, or equal day and night in spring; but it is
the Australian autumnal equinox. In September the Australias have the
spring equinox, and the English the autumnal. The sun is seen overhead
to the furthest north on the 21st of June, and to the furthest south on
the 21st of December.
Why, the first is the summer of England, and the last the winter. Then
I suppose that is the reason why in summer the sun looks so high up at
noon. Then in winter, as it is shining more over parts south of the
equator, the north would neither see nor feel so much of him.
That is correct. You now see why the Australian summer is at the time
of the English winter.
Yes, father; because they are on opposite sides of the equator. But you
know that the sun does not really move about like this. I want to know
what does move.
The earth, to be sure.
I understand that; but neither the rotundity nor motion seems
to explain this mystery of the Zodiac. But let me see. When the
world swings round the master light, is it obliged to keep bolt
upright--north pole up and south pole down?
How would your equator then be, James?
Right opposite the sun. But that will not do, for it is not always
opposite to the sun. Perhaps the world goes waddling along like a duck,
first on one side a little bit, and then on the other. This would bring
the sun opposite to either place.
It would be a very regular waddle. We will try your scheme. Pick up
that round wooden ball there. Carry it round the capstan, and see
whether by twisting it from one side to the other you can keep the
south pole shone upon for six months, and the north pole shone upon for
the other six months.”
James now makes a trial. But after all sorts of turns he failed in
producing the English winter and summer in the proper time and for the
proper length of time.
“I must give it up, father.
Just slant your ball a little out of the perpendicular, and carry it
round your sun without moving it from its position.
Capital! It explains the whole. When it was in front of the capstan,
the south pole was toward it; that was the Australian summer. When I
went to the right side, neither end was inclined toward it; this was
the sun over the equator. When I came to the back of it, the north pole
was toward it; this was the English summer. When I reached the left
side, my equator was opposite to it; this was the sun’s second crossing
of the Line. When I got to the front again, there was my south pole
pointing to the capstan again.
Then you really understand the seasons. Of course the spring in England
is the autumn of Australia. But I have something else to recall to your
recollection. Have you forgotten the old church on the hill at home?
No, father, and never shall. How pretty it looked when the sun rose
over it upon a fine spring morning, with the birds all alive with their
song, and the bees down upon the flowers!
Did the sun rise over the church at hay harvest?
No; I remember then it came up from behind the squire’s house to the
left of it.
Where was the sun first seen upon a cold winter’s morning?
Aye, I fancy I see his red face looking lazily over the parsonage to
the right of the church, and that when we had done breakfast, too.
How came the sun to jump about in that manner?
Why, do you see, he did not hop from one side to the other. He would
get a little further from the church each morning till he rose over the
squire’s house: then, as if ashamed, he seemed to creep back to his old
place. Afterwards he appeared to take it into his head gradually to get
on to the parsonage, and then he would once more turn to the church.
Which was on the north-side of the church, James?
The squire’s house. Now, I think I can explain all without your
questions this time, my dear father.
Then go on by all means.
The sun rose over the squire’s house in summer, for that was the north
side; the north pole was then inclined to the sun. At spring it was
half-way between the squire’s and the parsonage; this was the sun over
the equator. In winter the sun rose at the furthest part to the south;
this was where the north pole was turned away, and the south side
turned to the sun.
Well, then, you have satisfactorily explained the seasons.”