This current warms the air and makes the climate milder, and it keeps the
water from freezing, so that shipping is carried on all winter,"
Lieutenant Ekman explained.

Just then a sailor came to tell them that their dinner was ready. While
they were eating, the launch made a landing at the first of the
lighthouses which the inspector had to visit.

While their father was busy, the twins clambered over the rocks, hunting
for starfishes and sea-urchins, and Gerda picked a bouquet of bright
blossoms for their table on the boat.

At the next stopping-place, which was Gefle, the captain took them on
shore to see the shipyard where his own launch, the _North Star,_ was
built; and so, all day long, there was something to keep them busy.

As the boat steamed farther north, each new day grew longer, each night
shorter, until Birger declared that he believed the sun did not set at
all.

"Oh, yes it does," his father told him. "It sets now at about eleven
o'clock, and rises a little after one. You will have to wait until you
cross the Polcirkel and get to the top of Mount Dundret before you have a
night when the sun doesn't even dip below the horizon."

"We must be pretty near the Arctic Circle now," exclaimed Gerda. "It is
growing colder and colder every minute."

"That is because the wind is blowing over an ice-floe," said her father,
pointing to a large field of ice which seemed to be drifting slowly