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Exceptional, early laboratory notes written and signed twice by Thomas Edison, "T. A. Edison" and "Edison," one page, 9 x 11.75, September 30, 1877. Edison sketches an experimental version of his "Speaking Telegraph"—an early telephone transmitter and receiver designed to transmit voice electrically—with a handwritten explanation below, in full: "I propose to place a rubber diaphragm in a Bell Telephone, streatch it tight & let his present diaphragm lean upon it loose, i.e. not thoroughly or fastened at edges this will dampen it & prevent harmonics, have tried it out OK." Additionally signed at the top by his longtime assistant, Charles Batchelor, who famously supported Edison in some of his most important projects in the fields of telegraphy, telephony, and electric lighting. In good to very good, fragile condition, with light staining and soiling, edge chips and tears, and splitting to the folds.
Following Alexander Graham Bell’s 1876 Centennial Exposition demonstration, Edison believed the telephone to be fundamentally flawed—particularly its inability to transmit clearly over long distances—and set out to remedy its acoustic limitations. Assisted by Charles Batchelor, who conducted many of the auditory tests due to Edison’s near deafness, Edison experimented with diaphragms, mouthpieces, and resistance-altering materials throughout 1877. The present laboratory notes record a significant breakthrough: Edison’s use of a rubber diaphragm to dampen harmonics and improve vocal clarity. Edison’s concluding note—“Have tried it OK”—highlights the practical success of the experiment. A sought-after, tangible record of Edison’s hands-on engineering process, documenting a significant experiment in the evolution of electronic voice transmission.
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