Year: 1879

phone-The Miscrophone, etc.


North American Review: Elec-


trio incandescence, as a source of


light, was first reduced to q prac-


tical shape about twenty years ago


by NJ. de Changy in Paris, and by


Mr.. Moses O.. Farmer in Salem,


Mass. Both of these gentlemen


seem to have developed electric


lamps operating by the incandes-
ceEce of a metallic wire, and having


an efficient automatic regulator by


which their coEstancy of action was
! secured; but the great cost of cleo
tricity, produced at that time by
the galvanic battery, caused the
abandonment of all efforts to make
any practical use of such apparatus


Now, however, that a relatively
cheap source of electricity is found
in the magnetic electric machine,
these old plans have been revived,
and we find in Mr.. Edison's Eng
lish patents redevelopment of the
same thing.


They all operate on the fact that
when a powerful current of elec
tricity traverses an insufficient con
ductor, as wire or narrow strip of
platinum, for example, the same is
intensely heated, and so becomes
luminous. Coils of wire, strips of
platinum, or the like, are therefore
so arranged that a current shall
pass through them, and SO make
them luminously hot or incandes-
cent. AS this incandescence is
greatest near the fusing point of
these substances, and their fusion
would of course interrupt the ac-
tion, various ingenious contrivances
are adopted by which the current is
automatically shut off or diverted
if it approaches too near to this dis
astrous result. Thus, for example,
the strip of incandescent metal it.
self so operates lever that as soon
as its expansion reaches a certain
degree it closes a circuit, which di
verts part of the current into an
other conductor.


There are a multitude of these
contrivances, and almost every day
sees new ones added to the list, but
so far they have all been very elab-
crate, often complicated, and as a
rule, expensive instruments.


Another plan is to use, in place
of metal which may be fused, a
thin rod of carbon, which can not
be fused and whose tendency to
burn is overcome by inclosing it in
glass vessel filled with some gas
which cannot combine with it, nj
trogen for example. Lamps OF this
nature have been largely expert
mented with, and inventors are still
laboring upon them, but as yet the
success obtained is not such as to
warrant their practical Introduction
into actual use.


In all plans of obtaining light by
electric incandescence so far pub
lished, the cost of the light has been
many times greater than with an
electric arc.


On the other hand, by incandes-
cence, lights of moderate power,
equal, for example, to one or two
gas burners, can be produced, and
this would be of course a property
of essential Importance In any gen-
e-al use of electricity for domestic |
lighting.


It is on these subjects that sew
eral of the most ingenious minds Of !
the day are now working, and what
we have above stated not only gives
the present state of the problem, but
will prepare the reader to compre-
hend the new developments as they |
appear.


The next application of Fara-
days discovery of magnetic Undue
tion is found IN the Bell telephone. |
In this instrument q series of elec- |
tric currents is developed by the,
movements of thin plate of iron
in front of a steel magnet, around
whose end a wire is coiled. AS the
thin iron plate vibrates to the i'm
pulse received from the voice of one
speaking near it, the lines of force
about the magnet are caused to
move, and so cut across the coils of
wire, and consequently develop in
them electric currents. These fuc
tuating electric currents, carried by
telegraph wire to distant place,
modify as they vary, the attraction
of a similar magnet for like thin
iron plate, and thus this plate re-
peats the motions of the first one,
and gives to the ear of the listener
the motions which constituted the
sounds in the spoken words uttered
against the first iron plate.


Notifications in form or arrange
ment of parts have been made by
various experimenters and invent
ors, but the same principle pervades
all the telephones of this class.