. But it is a singular fact that a nation will perfectly
understand some art or manufacture that seems absolutely necessary to
men's comfort and convenience, and yet this art in time will be
completely lost, and things that were in common use will pass as
completely out of existence as if they had never been, until, in after
ages, some of them will be found among the ruins of cities and in old
tombs. In this way we have found out that ancient nations knew how to
make a great many things that enabled them to live as comfortably and
luxuriously as we do now. But these things seem to have perished with
the nations who used them, and for centuries people lived
comfortlessly without them, until, in comparatively modern times, they
have all been revived.

Glass-making is one of these arts. It was known in the early ages of
the world's history. There are pictures that were painted on tombs two
thousand years before Christ's birth which represent men blowing
glass, pretty much as it is done now, while others are taking pots of
it out of the furnaces in a melted state. But in those days it was
probably costly, and not in common use; but the rich had glass until
the first century after Christ, when it disappeared, and the art of
making it was lost.

[Illustration]

The city of Venice was founded in the fifth century, and here we find
that glass-making had been revived. You will see by this picture of a
Venetian bottle how well they succeeded in the manufacture of glass
articles.

Venice soon became celebrated for this manufacture, and was for a long
time the only place where glass was made. The manufacturers took great
pains to keep their art a secret from other nations, and so did the
government, because they were all growing rich from the money it
brought into the city.

In almost any part of the world to which you may chance to go you
will find Silica. You may not know it by that name, but it is that
shining, flinty substance you see in sand and rock-crystal. It is
found in a very great number of things besides these two, but these
are the most common.

Lime is also found everywhere--in earth, in stones, in vegetables and
bones, and hundreds of other substances.

Soda is a common article, and is very easily produced by artificial
means. Potash, which has the same properties as soda, exists in all
ashes.

Now silica, and lime, and soda, or potash, when melted together, form
glass. So you see that the materials for m