ptain?" enquired 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 clearing away and
washing up the debris 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 hout
'ere?"

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 surface the whole volume of it must be cooled
down to 40 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 the meaning of the
explanation, "'ow very hodd. But can you tell me, Mr Saunders, 'ow it
is that them 'ere hicebergs is made? Them's wot I don't comprehend no
'ow."

"Ay," replied Saunders, "there has been many a wiser head than yours
puzzled for a long time aboot icebergs. But if ye'll use yer eyes
you'll see how they are formed. Do you see the high cliffs yonder away
to the nor'-east? Well, there are great masses o' ice that have been
formed against them by the melting and freezing of the snows of many
years. When these become too heavy to stick to the cliffs, they tumble
into the sea and float away as icebergs. But the biggest bergs come
from the foot of glaciers. We know what glaciers are, Mivins!"

"No, sir, I don't."

The second mate sighed. "They are immense accumulations of ice, Mivins,
that have been formed by the freezings and meltings of the snows of
hundreds of years. They cover the mountains of Norway and Switzerland,
and many other places in this world, for miles and miles in extent, and
sometimes they flow down and fill up whole valleys. I once saw one in
Norway that filled up a valley eight m