heir motion, to guide them. Now, unless at the end of the voyage they
should come out precisely right at the lighthouse or at the harbor which
they aim at, they might get into great difficulty or danger. They might
run upon rocks where they expected a port, or come upon some strange
and unknown land, and be entirely unable to determine which way to turn
in order to find their destined haven.

The navigators could, however, manage this all very well, provided they
could be sure of seeing the sun every day at proper times, particularly
at noon. The sun passes through different portions of the sky every
different day of the year, rising to a higher point at noon in the
summer, and to a lower one in the winter. The place of the sun, too, in
the sky, is different according as the observer is more to the northward
or southward. For inasmuch as the sun, to the inhabitants of northern
latitudes, always passes through the southern part of the sky, if one
person stands at a place one hundred or five hundred miles to the
southward of another, the sun will, of course, appear to be much higher
over his head to the former than to the latter. The farther north,
therefore, a ship is at sea, the lower in the sky, that is, the farther
down toward the south, the sun will be at noon.

Navigators, then, at sea, always go out upon the deck at noon, if the
sun is out, with a very curious and complicated instrument, called a
sextant, in their hands; and with this instrument they measure exactly
the distance from the sun at noon down to the southern horizon. This is
called making an observation. When the observation is made, the captain
takes the number of degrees and minutes, and goes into his state room;
and there, by the help of certain tables contained in books which he
always keeps there for the purpose, he makes a calculation, and finds
out the exact latitude of the ship; that is, where she is, in respect to
north and south. There are other observations and calculations by which
he determines the longitude; that is, where the ship is in respect to
east and west. When both these are determined, he can find the precise
place on the chart where the vessel is, and so--inasmuch as he had
ascertained by the same means where she was the day before--he can
easily calculate how far she has come during the twenty-four hours
between one noon and another. These calculations are always made at
noon, because that is the time for making the observations