ept that a strip of gelatine takes the place of hard rubber, as
the sensitive member. Besides being affected by heat, this device is
exceedingly sensitive to moisture. A few drops of water or perfume
thrown on the floor of a room are sufficient to give a very decided
indication on the galvanometer in circuit with the instrument.
Barometers, hygrometers, and similar instruments of great delicacy can
be constructed on the principle of the odoroscope; and it may also be
used in determining the character or pressure of gases and vapors in
which it has been placed.

In the list of Edison's patents at the end of this work may be noted
many other of his miscellaneous inventions, covering items such as
preserving fruit in vacuo, making plate-glass, drawing wire, and
metallurgical processes for treatment of nickel, gold, and copper ores;
but to mention these inventions separately would trespass too much on
our limited space here. Hence, we shall leave the interested reader to
examine that list for himself.

From first to last Edison has filed in the United States Patent
Office--in addition to more than 1400 applications for patents--some
120 caveats embracing not less than 1500 inventions. A "caveat" is
essentially a notice filed by an inventor, entitling him to receive
warning from the Office of any application for a patent for an invention
that would "interfere" with his own, during the year, while he is
supposed to be perfecting his device. The old caveat system has now been
abolished, but it served to elicit from Edison a most astounding record
of ideas and possible inventions upon which he was working, and many
of which he of course reduced to practice. As an example of Edison's
fertility and the endless variety of subjects engaging his thoughts, the
following list of matters covered by ONE caveat is given. It is needless
to say that all the caveats are not quite so full of "plums," but this
is certainly a wonder.

Forty-one distinct inventions relating to the phonograph, covering
various forms of recorders, arrangement of parts, making of records,
shaving tool, adjustments, etc.

Eight forms of electric lamps using infusible earthy oxides and brought
to high incandescence in vacuo by high potential current of several
thousand volts; same character as impingement of X-rays on object in
bulb.

A loud-speaking telephone with quartz cylinder and beam of ultra-violet
light.

Four forms of arc light with special carbons.