Phonograph.
An apparatus for reproducing articulate speech. It is not electric,
except as it may be driven by electricity.
It consists of a cylinder of wax-like material which is rotated and
moved slowly, longitudinally, screw fashion, at an even speed. A glass
diaphragm carrying a needle point is supported with the point barely
touching the wax. If the diaphragm is agitated, as by being spoken
against, the needle is driven back and forwards cutting a broken line or
groove following the direction of the thread of a screw in the wax, the
depth of which line or groove continually varies.
This imprints the message. If the needle is set back and the cylinder is
rotated so as to carry the needle point over the line thus impressed,
the varying depth throws the needle and diaphragm into motion and the
sound is reproduced.
The cylinder is rotated often by an electric motor, with a centrifugal
governor.
[Transcriber's note; Due to T. A. Edison, 1877, fifteen years before
this book.]
Phonozenograph.
An apparatus for indicating the direction of the point where a sound is
produced. It operates by a microphone and telephone in conjunction with
a Wheatstone bridge to determine the locality.
Phosphorescence.
The emission of light rays by a substance not heated, but whose
luminosity is due to the persistence of luminous vibration after light
has fallen upon it.
A phosphorescent body, after exposure to light, is luminous itself.
Phosphorescence may be induced by rubbing or friction, by heat, by
molecular bombardment, as in Crookes' tubes, and by static discharge of
electricity, as well as by simple exposure to light.
Another form of phosphorescence may be due to slow chemical combustion.
This is the cause of the luminosity of phosphorous.
Phosphorous, Electrical Reduction of.
Phosphorous is reduced from bone phosphate by the heat of the electric
arc. The phosphate mixed with charcoal is exposed to the heat of the
voltaic are, and reduction of the phosphorous with its volatilization at
once ensues. The phosphorous as it volatilizes is condensed and
collected.
Photo-electricity.
The development of electrical properties by exposure to light. Crystals
of fluor spar are electrified not only by heat (see Pyro-electricity)
but also by exposure to sunlight or to the light of the voltaic arc.
[Transcribers note: Although first observed in 1839 by Becquerel, it
was not explained until 1905 by Albert Einstein with the introduction of
photons.]
Photo-electric Microscope.
A projection, solar or magic-lantern microscope worked by the electric
light.
Photo-electro-motive Force.
Electro-motive force produced in a substance by the action of light.