outline. The subject is also old, yet to every boy it must be told
again, and the most ordinary intelligence must have some desire to know
the secrets, if such they are, of that which is unquestionably the
greatest force that ever yielded to the audacity of humanity. It is now
of little avail to know that all the records that men revere, all the
great epics of the world, were written in the absence of the
characteristic forces of modern life. A thousand generations had lived
and died, an immense volume of history had been enacted, the heroes of
all the ages, and almost those of our own time, had fulfilled their
destinies and passed away, before it came about that a mere physical
fact should fill a larger place in our lives than all examples, and that
the evanescent vapor which we call steam should change daily, and
effectively, the courses and modes of human action, and erect life upon
another plane.

It may seem not a little absurd to inquire now "what is steam?"
Everybody knows the answer. The non-technical reader knows that it is
that vapor which, for instance, pervades the kitchen, which issues from
every cooking vessel and waste-pipe, and is always white and visible,
and moist and warm. We may best understand an answer to the question,
perhaps, by remembering that steam is one of the three natural
conditions of water: ice, fluid water, and steam. One or the other of
these conditions always exists, and always under two others: pressure
and heat. When the air around water reaches the temperature of
thirty-two degrees by the scale of Fahrenheit, or or zero by the
Centigrade scale, and is exposed to this temperature for a time, it
becomes ice. At two hundred and twelve degrees Fahrenheit it becomes
steam. Between these two temperatures it is water. But the change to
steam which is so rapid and visible at the temperature above mentioned
is taking place slowly all the time when water, in any situation, is