THE WORLD OF ICE. 15

“What is a water-sky, captain ?” inquired Fred.

“It is a peculiar, dark appearance of the sky on
the horizon, which indicates open water ; just the
reverse of that bright appearance which you have
often seen in the distance, and which we call the ice-
blink.”

“We'll have open water soon,” remarked the second
mate authoritatively.

“Mr. Saunders,” said Mivins, who, having just
finished cleaving away and washing up the débris
and dishes of one meal, was enjoying in complete
idleness the ten minutes of leisure that intervened
between that and preparations for the next——“Mr.
Saunders, sir, can you hinform me, sir, ow it is that
the sea don’t freeze at ‘ome the same as it does out
ere 2”

The countenance of the second mate brightened, for
he prided himself not a little on his vast and varied
stores of knowledge, and nothing pleased him so
much as to be questioned, particularly on knotty
subjects.

“Hem! yes, Mivins, I can tell ’ee that. Ye must
know that before fresh water can freeze on the sur-
face the whole volume of it must be cooled down to
#0 degrees, and salt water must be cooled down to 45
degrees. Noo, frost requires to be very long continued
and very sharp indeed before it can cool the deep sea
from the top to the bottom, and until it is so cooled it
canna freeze.”

“Oh!” remarked Mivins, who only half understood