OMPASS, BAROMETER, THERMOMETER, WATCHES,
CLOCKS, TELESCOPE, MICROSCOPE, GUNPOWDER, STEAM ENGINE, AND
ELECTRO-MAGNETIC TELEGRAPH.

When were Spectacles invented, and who was their inventor?

It is supposed that they were first known about the thirteenth
century, and invented by a monk of Pisa, in Italy, named Alexander de
Spina. Spectacles are composed of two circular pieces of glass set in
a frame.

What are these glasses called?

Lenses. They are either convex or concave, according to the kind of
sight requiring them. Old people, and those who can only see things at
a distance, from the flatness of the eye, which prevents the rays of
light converging so as to meet in the centre, require convex lenses.
People who can only distinguish objects when viewed closely, from the
eye being too convex, require concave lenses to counteract it by
spreading the rays, and thus rendering vision distinct.

_Convex_, rising outwardly in a circular form; opposite to
concave.

_Concave_, hollow; round, but hollow, as the inner curve of
an arch, &c.

_Converging_, tending to one point from different parts.

_Vision_, the faculty of seeing.

What is the Mariner's Compass?

A most useful and important instrument, by the aid of which the
navigator guides his ship on the sea, and steers his way to the place
of his destination. The inventor of the Mariner's Compass is not
known, nor the exact time of its introduction; it was employed in
Europe in navigation about the middle of the thirteenth century, and
has been in use more than five hundred years. The Chinese are said to
have been acquainted with it much earlier, but no reliance can be
placed on their dates. The power of the loadstone to attract iron was
known to the ancient Egyptians, but it was not applied to any
practical purpose.

_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 w