a fire-alarm telegraph
system embodies a central office to which notice can be sent
from any number of signal boxes of the outbreak of a fire in
the district covered by the box, the central office in turn
calling out the nearest fire engines, and warning the fire
department in general of the occurrence. Such fire alarms
can be exchanged automatically, or by operators, and are
sometimes associated with a large fire-alarm bell or
whistle. Some boxes can be operated by the passing public;
others need special keys. The box mechanism is usually of
the ratchet, step-by-step movement, familiar in district
messenger call-boxes.]

Edison's curiously practical, though imaginative, mind demanded
realities to work upon, things that belong to "human nature's daily
food," and he soon harked back to telegraphy, a domain in which he
was destined to succeed, and over which he was to reign supreme as
an inventor. He did not, however, neglect chemistry, but indulged his
tastes in that direction freely, although we have no record that
this work was anything more, at that time, than the carrying out of
experiments outlined in the books. The foundations were being laid for
the remarkable chemical knowledge that later on grappled successfully
with so many knotty problems in the realm of chemistry; notably with
the incandescent lamp and the storage battery. Of one incident in his
chemical experiments he tells the following story: "I had read in a
scientific paper the method of making nitroglycerine, and was so fired
by the wonderful properties it was said to possess, that I determined
to make some of the compound. We tested what we considered a very small
quantity, but this produced such terrible and unexpected results that we
became alarmed, the fact dawning upon us that we had a very large
white elephant in our possession. At 6 A.M. I put the explosive into
a sarsaparilla bottle, tied a string to it, wrapped it in a paper,
and gently let it down into the sewer, corner of State and Washington
Streets." The associate in this was a man whom he had found endeavoring
to make electrical apparatus for sleight-of-hand performances.

In the Boston telegraph office at that time, as perhaps at others, there
were operators studying to enter college; possibly some were already in
attendance at Harvard University. This condition was not unusual at one
time; the first electrical engineer graduated fr