New-York tribune., 1878-06-08
TELEPHONE AND MICROPHONE.
LETTER FROM THOMAS A. EDISON.


LETTER FROM THOMAS A. EDISON.
THE QUESTION OF PRIORITY OF INVENTION
BETWEEN HIM AND PROFESSOR HUGHES. OF
LoNDoN-NR. EDISON CLAIMS VIOLATION OF
HIS RIGHTS, AND BREACH OF CONFIDENCE
BETWEEN FRIENDS
To he Editor Of The Tribune
SIR: Allow me to make few observations upon
an editorial article which appeared in yesterday 5
IRIBINE upon the recent claims advanced by Pro-
fessor d. +. Hughes, of London, to the invention of
the leading features of my carbon telephone, and Of
my micr0tasimeteT or instrument for the measure
ment Of minute degrees of heat.
You have attributed TO Professor Hughes two inn
proyements upon my methods of preparing the car
bon buttons Tor the telephone, namely: in the
metalzatiOn of the carbon by plunging it in mer-
cury, and the division Of the carbon into several
pieces. Your suppostion that the latter process
not identical with my of gas-Tetort carbon is
perfectly correct but the subdivision of the carbon
had been repeatedly tested by me in my experiments
on the telephone especially in a series conducted
at the special request of President Orion shortly
before his DEATH of which the illustrative drawings
were seen at the time by several persons, and are
still in my possession. The metallIzation of the
carbon by punging il in mercury Is also a process
perfectly familiar to me- having been employed IN
many Of my telephone experiments Of last year.
and, though mercury is not specially named, II Is
clearly included in the expression finely divided
metals" which occurs in the memoranda furnished
Mr.. Geo. b. Prescott for his forthcoming work on
"The Speaking Telephone" as printed in The Jour
nal Of The IcicCraDh FOR the 10th Of April last Mr.
Hughes seems to have been so impressed with this
phrase that he employs it repeatedly speaking OF
mercury in iinely divided state.D OF " holding
the mercury in a line state OF DIVISION OF metal
disributed-n in a fine state of division" Of iron in
a fine state Of division :" again. Of the minute di
vision Of the ron." and lastly of "a platinum sur
face III a finely divided state"
The change Of electrical resistance with enoT-
nous rapidity by plumbago under pressure was
a discovery of my own. distinctly set forth IN my
application for patent for an Improvement in
speaking telcgaphs," dated July 20, 1877, as pub
lished al the time in The philadelphia Press and The
Scientific Amo1caR July 2s. 1870. This discovery
evidently covers the principle claimed his own
by Professor Hughes. He says: 1T is quite
evident that these effects due to difference OF
pressure at the different points Of cOntacr-wmch Is
precisely the principle Of my carbon telephone, thus
set forth months ago by Mr. Geo. Il. Prescott IN
the aforementioned volume: BY yconstant expert
menting however. Mr. Edison at length made the
discovery that when properly prepared, carbon
possessed the remarkable property Of changing its
resistance with pressure and that the ratios OF
these changes, mOrcver, corTesp0nded exactly with
tie pressure"
You consider as the most striking difference be-
tween my telephone and the instrument ol Professor
Hughes that in the latter the diaphragm is dis
pensed with. In his own words: d" IL viii be seen,
however that in the experiments made by myself,
the diaphragm has been altogether discarded. rest
ing rs II does upon the changes produced by mole
cuar action and that the variations IN the strengths
Of the currents flowing are produced simply and
solely by the direct effect Of the sonorous vibra-
tionsr
The following extract from AIr. Prescotrs book. as
gwen Ia The Journal oCihe Telegraph April 16 1878,
Will show that the discardng Of the diaphragm is
my own invention:
in Of transmitter which Mr. Edison has
introduced The vibrating diapbra-m y done ny WIN
atocrhcrt haNing bcrD i'uhd tti much Delef tcsi'.
obtained when ryd plate OF metal u substituted
an its place. Win the old vibrating diaphragm the
articulation produced ln the rceter y more OF ess
D. lgird owing slight changes which the vibrating
di.A occasion, 10 ne pressure ah" %hch pIoPaDy re-
suits nom tlrdy daWpcning OF the Ylbtfons altf nav
ing been once started. IT. the arrangement, how
ever the aiticulluon j. clear aud exceedingly we'll
rendered thai whisper even ht ie'iiY ne Transmitted
and uudcr- stood. Tie icLtbc plate, OF COURSE merely
serves m consequence u IT. comparatively large area
b. concentrate considerable potion OF the s0nOrous
waves upon tie small carbon disk or button; much
rt OF the speaker thus brought bear tho disk
han could be 05aiHed u ony its small surface alone re
ussd.
The claim of Professor Hughes to the discovery
that modification Of his micophone can be used
a measure of minute degrees Of heat is still more
prcposterous than the preceding This is discovery
of mine, which was first announced III Tie WGshiHg-
tou Star of the 18th of April last. copy of that
paper was sent by Inc to Mr. W. H. Precce, the CO.
adiutor Of Professor Hughes in this pretended
invention" and have positive evidence that it
reached him before the presentation Of the so-caled
"mIcrophone to the ROYAL Society, inasmuch as
he has made an extract from II IN his address OF
Nav before the London Society of Arts.
MIR w H. Preece, electrician to the London Post
Office Department, was iu this country ma the early
part of last year. aud visited my laboratory. /
freely showed HIM the experiments was then max
ing including the principle of the carbon telephone
and the variability Of conducting power IN many
substances under pressure. made him my agent
for the presentation of this telephone, and subse-
quently of the phOnOgTaph, IN Lngiand and Kept
him informed. by copies OF publications and by PR
vate letters, of my leading experiments, as he al
WAYS manifested great desire 10 be the means OF
preseutlng my discoveries TO the British public.
/ therefore regard the conduct of Mr. Preece in
tins matter ~ not merely violation of my rights
ms AN inventor. but as gross infringement OF the
confidence obtained under the gulse OF friendship
Yours very truly, THOMAS A. EDISON.
Meai0 Park y. j., June g, 1878.