mpass. A graduated arc is fitted to it so that the amount of dip at
any place on the earth's surface can be ascertained. At the magnetic
equator there is no dip at all, because the needle being equally distant
from the north and south magnetic poles, remains horizontal. As you
travel north the needle dips more and more until it reaches the region
of the north magnetic pole when it is almost perpendicular--pointing
straight down.

"Now, it is only on a very few places of the earth's surface that the
horizontal needle points to the true north and south, and its deviation
from the _earth's_ pole in its determination to point to the _magnetic_
pole is called the variation of the compass. This variation is greater
or less of course at different places, and must be allowed for in
estimating one's exact course. In our present explorations we have got
so far beyond the beaten track of travel that greater allowance than
usual has to be made. In fact we have got considerably to the north of
the magnetic pole. At the same time we are a good way to the east'ard
of it, so that when I see the compass with its letter N pointing to what
I know to be the magnetic north, I take our geographical position into
account and steer almost due east by _compass_, for the purpose of
advancing due north. D'ye see?"

"I'm not so sure that I do, father. It seems to me something like the
Irishman's pig which you pull one way when you want him to go another.
However, I'll take your word for it."

"That's right, my boy; when a man can't understand, he must act on
faith, if he _can_, for there's no forcing our beliefs, you know.
Anyhow he must be content to follow till he does understand; always
supposing that he can trust his leader."

"I'm out of my depths altogether now, father. P'r'aps we'd better
change the subject. What d'ye say to try a race with Leo? His boat
seems to be overhauling us."

"No, no, Ben; no racing. Let us advance into the great unknown north
with suitable solemnity."

"We appear to sail rather better than you do, uncle," shouted Leo, as
his boat drew near.

"That's because you're not so heavily-laden," replied the Captain,
looking back; "you haven't got giants aboard, you see; moreover there's
one o' you rather light-headed."

"Hallo! uncle; evil communications, eh? You'd better change Benjy for
Oblooria. She's quite quiet, and never jokes. I say, may I go ahead of
you?"

"No, lad, you mayn't. Take a r