n the summer with the sun shining on her head at
the North Pole," and a grandmotherly-looking figure in a Raettvik costume
was quickly hung up on the line of the orbit, her head tipped toward the
sun.

"Here she is again in winter, with the sun shining on her feet at the
South Pole," and Gerda drew the figure on the opposite side of the orbit
with her head tipped away from the sun.

"That is exactly how it is," said her father. "But do you understand
that, when she is slowly moving round the sun, she is always tipped in
the same direction, with the North Pole pointing toward the north star;
so there comes a time, twice a year, when her head and her feet are both
equally distant from the sun, which shines on both alike?"

"No," said Gerda. "When does that happen?"

"It happens in March and September, when Mother Earth has travelled just
half the distance between summer and winter."

"Oh, I see! This is where she would be;" and Gerda made two dots on the
orbit, each half-way between the two grandmothers.

"Good," said her father. "Now when she is in that position, day and
night, all over the earth, are each twelve hours long. We call them the
'Equinoxes.' It is a Latin word which means 'equal nights.'"

"In March and September do we have a day when it is twelve hours from
sunrise to sunset, and twelve hours from sunset to sunrise?" questioned
Gerda.

"Yes, and it is the same all over the earth the very same day," repeated
Lieutenant Ekman. "If you will look in the almanac when you go home, you
will see just which day it is."

Gerda studied her drawing for a few minutes in silence. "I think I
understand it now," she said at last.

"It is easy to understand after a little study," her father told her;
"but everyone has to see it for himself, just like the midnight sun.

"When the North Pole, or Fru Earth's head, is turned toward the sun we
have the long summer days in Sweden. When it is turned away from the sun
we have the long winter nights. The nearer we go to the pole, the longer
days and nights we have. If we could be directly at the pole, we should
have six months of daylight and six months of darkness every year."

"What did you say?" asked Birger, who came around the corner of the hut
just in time to hear his father's last words.

"We were explaining how it is that the farther north we go in summer, the
longer we can see the sun each day," said Gerda.

"Let me hear you explain it," suggested Birger, tr