"Nonsense!" exclaimed Sigrid loyally. "They will never forget their
friends. Besides, I like Karen myself. Let's go and see her now. She must
be lonely without Gerda."

In the meantime the little party of four--Lieutenant Ekman, with Erik and
the twins--were sailing across the eastern end of Lake Mälar toward the
Södertelje Canal.

Birger and Gerda explored the boat, making friends with some of the
passengers, and then found seats with Erik on the forward deck, where
they could see the wooded shore of the lake. They passed many an island
with its pretty villas peeping out among the green trees, and saw gay
pleasure parties sailing or rowing on the quiet water.

In a short time the boat sailed slowly into the peaceful waters of the
Södertelje Canal. This is the first of the short canals which form links
between the lakes and rivers of Southern Sweden, thus making a shorter
waterway from Stockholm to Göteborg; and while the trip is about three
hundred and seventy miles long, only fifty miles is actual canal, more
than four-fifths of the distance being covered by lakes and rivers, with
a fifty-mile sail on the Baltic Sea.

The principal difficulty in making this waterway across Sweden lay in the
fact that the highest of the lakes is about three hundred feet above the
sea level, and the boats have to climb up to it from the Baltic Sea, and
then climb down to Göteborg. This climbing is accomplished by means of
locks in the canals between the different lakes. In some canals there is
only one lock, but in others there are several together, like a flight of
stairs. There are seventy-six locks in all.