Navigator, one who guides a ship.

     Steer, to direct or guide a vessel in its course.

     Destination, the place to which a person is bound.

     Practical, capable of practice, not merely speculative.

What is the Loadstone?

An ore of iron which possesses the peculiar property of attracting iron, namely, of drawing it in contact with its own mass, and holding it firmly attached by its own power of attraction.  A piece of loadstone drawn several times along a needle, or a small piece of iron, converts it into an artificial magnet; if this magnetized needle is carefully balanced, it will 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?