New-York tribune., 1878-06-05
TrIRPUOYE and MICROPHONE.

A ouestiOn of priority of invention seems hkely
10 be started between Mr.. Thomas A. Edison and
Professor d. T. Hughes, concerning the device
which the latter has called the micro
phone" As nearly as we have Deen
able 70 ascertain the facts, they may be
summed up rs follows: Professor Hughes has
displayed and described before the Royal Society,
Londor an instrument for magnifying sounds, by
which, for instance the tramp of fly may be rem
dered audible and may be heard through
n telephone, miles away. The substance used In
this instrument for increasing sound. is carbon
through which an electric current is passing. Now
Mr. Edison invented more than a year ago his
"carbon telephone" There is no doubt that
he WAS the first to discover remarkable
property of carbon-that its capacity for conduct
ing electricity may he very largely varied by small
differences of pressure applied to the carbon ITSELF
This singular property Is made use OF in both
the Edison telephone and the Hughes microphOne
Such small differences of pressure as sound waves
can produce, serve the purpose of altering the flow
of an electric current in both inventions. so far,
Mr. Edison has every advantage of priority.
In two particulars however, Professor Hughes
prepares the carbon differently from the earlier de-
vices. His best successes were obtained when
the substance was metaized" by plung-
ing It in mercury after being heated to
whiteness; but it does not appear that
the carbon underwent any such process in
some of his experiments; on this point the
accounts given are not perfectly definite.
Both inventors tested many different sub
stances, and both decidedly preferred carbon.
Among the things which Mr.. Edison tried
were metals finely divided and Also tufts of fibre
coated with metal by chemical means; both these
methods have some similarity to that which Pro-
fessor Hughes employed ia the subdivision
of the material metal used. But it was in divid-
ing the carbon into two, three or four pieces that
the marvellous effects Of the microphone were
attained. and this does not appear to be the same
thing as, for instance Mr. Edson's use of
powdered gas-retort carbon. Professor Hughes
evidently thinks that the main power Of
his instrument is obtained by the use
Of separate pieces of carbon which are
lightly pressed together. His theory is that
sound wave causes the molecules of piece of car
bon to yibrate 80 that they and it take up moro
room, and hence press against larger surface
in the next piece. The greater the number of mole
cules thus brought close together in the sep
arate pieces of carbon, the greater will be
the Joint capacity of the pieces to carry the electric
current Professor Hughes illustrates this by
placing three or four pieces Of carbon IN tube,
barely touching each other in this condition they
will not convey electricity. But when waves of
sound affect these pieces the gaps between them are
so far closed that the electric current passes through
them readily. Thus 1t may depend upon the mere
pressure of the sound waves whether o strong cur
rent q moderate current. or no current at all,
shall pass over the wires to a delivering telephone.
In this way Professor Hughes appears to have Sc
cured o wide range Of power. In most
of his instruments he has been soicitous to shape
the pieces of carbon or other material that they
touch each other with rounded or pointed surfaces;
thereby getting the largest contacts with the
greater pressures and the smallest with the lesser
sound waves
The most striking difference between the instru-
ments of Mr.. Edison and Professor Hughes is that
in the latter the carbon is to be talked to direct
without the intervention of diaphragm
or metallic plate In recent article on the
subject in ScribRers Monthly Mr.. George Is.
Prescott says that all notifications Of the speaking
telephone "omploy diaphragm at the transmitting
end, capable of responding to the acoustic vibra-
tions Of the air." In one of the moro recent