perpendicular to her orbit, we should have twelve hours of daylight and twelve hours of darkness all over the earth every day in the year."

"I suppose she gets dizzy, spinning around so fast, and finds it hard to stand straight up and down," suggested Gerda.

"No doubt of it," answered her father gravely. "At least she has tipped over, so that in summer the North Pole is turned toward the sun, but in winter it is turned away from the sun."

"Let me show you how I think it is," said Gerda eagerly. She was always skillful at drawing pictures, and now she took the paper and pencil which her father gave her, and talked as she worked. "This is the sun and this is the earth's orbit," and she drew a circle in the center with a great path around it.

"This is Mother Earth in the summer with the sun shining on her head at the North Pole," and a grandmotherly-looking figure in a Rättvik 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, trying to find a comfortable seat on the rocky ground.

But Gerda drew a long breath of dismay. "Oh, Birger, you should have come sooner!" she exclaimed. "I understand it perfectly now; but if we go through it again I shall get all mixed up in my mind."

Lieutenant Ekman laughed. "I move that we stay up here and watch the midnight sun until we understand the whole matter and can stand on our heads and say it backwards," he suggested.

"I'm willing to stay all summer, if we can drive off in the daytime and see some Lapp settlements," said Birger, who had made friends with a young Laplander that morning at the Gellivare station.

"But it is daytime all the time!" cried Gerda. "When should we get any sleep?"

"I must be back in Stockholm by the middle of July," said Lieutenant Ekman; "but if your friend knows where there are some Laplanders not too far away, perhaps we can spare time to go and see them."

"Yes, he does," said Birger eagerly. "The mosquitoes have driven most of the herds of reindeer up into the mountains, but Erik's family are still living only a few miles north of Gellivare."

"What is Erik doing in Gellivare?" questioned Herr Ekman.

"He is working in the iron mines," Birger explained. "He wants to save money so that he can go to Stockholm and learn a trade. He doesn't want to stay here in Lapland and wander about with the reindeer all his life."

"So?" said Lieutenant Ekman in surprise. "Your friend Erik seems to have ambitions of his own."

"Look at Gerda!" whispered Birger suddenly.

Gerda sat on the ground with her back against the hut, and she was fast asleep. "Poor child," said her father, as he carried her into the hut and put her on a cot, "she has been awake all night. When she has had a little rest we will go back to Gellivare and look up your friend Erik. After we have all had a good night's sleep, we shall be ready to make a call on his family and their reindeer."