ill turn round of itself, till its end
points towards the North. The magnetized needle also possesses the
power of attracting iron, and of communicating this power to another
piece of iron or steel, similar to that of the loadstone itself.

_Contact_, touch.

_Magnetized_, rendered magnetic.

Describe the Mariner's Compass.

The Mariner's Compass consists of a circular box, enclosing a
magnetized bar of steel, called the _needle_, carefully balanced on an
upright steel pivot, and having that end which points to the North
shaped like the head of an arrow; attached to this needle, and turning
with it, is a card on which are printed the divisions of North, South.
East, and West; called the points of the compass. By simply looking at
the position of the needle, the mariner can see the direction in which
his vessel is sailing, and regulate his helm accordingly.

_Helm_, the instrument by which a ship is steered,
consisting of a rudder and tiller.

What is a Barometer?

An instrument for measuring the weight of the atmosphere, which
enables us to determine the changes of the weather, the height of
mountains, &c. It consists of a glass tube hermetically sealed at one
end, filled with mercury, and inverted in a basin of mercury;
according to the weight of the atmosphere, this mercury rises or
falls.

How is the Hermetic seal formed?

By heating the edges of a vessel, till they are just ready to melt,
and then twisting them closely together with hot pincers, so that the
air may be totally excluded. The word is taken from Hermes, the Greek
name for Mercury, the heathen god of arts and learning, and the
supposed inventor of chemistry,[9] which is sometimes called the
hermetical art; or perhaps from Hermes, an ancient king of Egypt, who
was either its inventor, or excelled in it.

[Footnote 9: See Chapter XVIII., article Chemistry.]

What is Mercury?

Quicksilver, or mercury, is a white fluid metal, the heaviest except
platina and gold; it readily combines with nearly all other metals,
and is used in the manufacture of looking-glasses, barometers,
thermometers, &c.; in some of the arts, and in the preparation of
several powerful medicines. It is found in California, Hungary,
Sweden, Spain, China, and Peru. The quicksilver mine of Guanca Velica,
in Peru, is one hundred and seventy fathoms in circumference, and four
hundred and eighty deep. In this profound abyss are seen streets,
squares,