| 6 January | Resolves two patent interference cases over acoustic multiple telegraphy designs with Elisha Gray by making and receiving formal concessions of priority on various points. |
| 8 January | Sketches several ideas for the application of small electric motors that could be marketed by American Novelty. |
| Mid-January | Begins extensive series of chemical and etheric force experiments. |
| 17 January | Begins two months of development work on a rotary, high-speed press for electric pen stencils, much of which is done by Charles Batchelor, who begins to resume role as Edison's chief experimenter. |
| With Charles Batchelor proposes a plan to George Bliss for establishing a foreign electric pen company. | |
| 18 January | Suit against Edison by former Newark landlords of American Telegraph Works, Ezra and Roscoe Gould, commences. |
| 19 January | Agrees with Charles Batchelor and Edward Johnson to assign his duplicating ink, Batchelor's door indicator, and Johnson's ribbon mucilage to American Novelty. |
| 20 January | First experiments with a telephone transmitter that varies electrical resistance of a circuit by changing the pressure on carbon rather than the amount of carbon. |
| 29 January | Proposes new agreement with Western Union for support of his laboratory. |
| Stockholders of the two competing Port Huron street railways agree to consolidation after receiving a proposal from Edison. | |
| 2 February | Complains to Jay Gould about his relations with Thomas Eckert and Atlantic and Pacific. |
| 3 February | Executes a patent application for an embossing recorder/repeater. |
| 8 February | Conducts first experiments with a two-plate embossing recorder/repeater. |
| 9 February | Western Union electrician George Prescott visits the Menlo Park laboratory to examine the recorder/repeater and Edison's telephones. |
| 15 February | Edward Johnson proposes name change from American Novelty Co. to Electro Chemical Manufacturing Co. |
| Mid-February | Begins sustained work on telephone. |
| 19 February | Urges Jay Gould to settle dispute with Western Union over rights to his quadruplex inventions. |
| 26 February | Anson Stager and George Bliss visit Menlo Park to discuss foreign rights to electric pen. |
| 28 February | Leaves for Port Huron to effect the merger of the Port Huron and Gratiot Street Railway Co. with the opposition line and to discuss his interest in the Sarnia Street Railway Co. with other stockholders. |
| Charles Batchelor accompanies Edison to Port Huron and then goes to Chicago to settle electric pen accounts with Western Electric, returning to Menlo Park on 8 March. | |
| 12 March | Returns to Menlo Park from Port Huron. |
| 14 March | Displays two-plate embossing recorder/repeater at Western Union headquarters in New York. |
| 18 March | Devises first electromotograph telephone receiver. |
| 19 March | Demonstrates his telephone instruments to Western Union officials in New York over a line to Menlo Park. |
| 21 March | Edison's father, Samuel, arrives in Menlo Park for a visit. |
| Winter–Spring | Experiments on waterproof varnishes for paper barrels for the New York Paper Barrel Co. |
| 22 March | Signs agreement with Western Union for regular financial support of the Menlo Park laboratory in exchange for all of Edison's future telegraph and telephone patents. |
| 23 March | Begins to prepare applications for a telephone patent and for a patent on his new sextuplex (six-message) telegraph system. |
| 30 March | Receives permission from William Orton to have Joseph Murray build six two-plate embossing recorder/repeaters. |
| 1 April | Devises telephone design that becomes the basis for his later claims to invention of the microphone. |
| 6 April | Laboratory staff's "pet" bear gets loose and they kill it. |
| 10 April | Begins experiments on telephone transmitter designs relying upon variations of pressure on semiconductors (primarily carbon) and devises pressure relay. |
| 18 April | Executes the first of his 1877 telephone patent applications. |
| 24 April | Signs agreement with Batchelor, George Bliss, and Charles Holland for marketing the electric pen in Europe. |
| 26 April | Begins testimony in New York in the "Quadruplex Case," Atlantic & Pacific v. Prescott and others. |
| 28 April | Begins week-long exhibition of his "musical" (electromotograph) telephone at the Newark Opera House. |
| 3 May | Finishes primary testimony in Quadruplex Case. |
| 16 May | Signs agreement with his nephew, Charles Edison, and former electric pen agent George Caldwell to exhibit his musical telephone. |
| 18 May | Visited at Menlo Park laboratory by British telegraph engineer William Preece. |
| 31 May | Begins month-long investigation of plumbago mixtures for telephone transmitter. |
| Signs an agreement with George Prescott and Gerritt Smith to pool their British quadruplex patents. | |
| 4 June | Electro Chemical Manufacturing transfers all of its duplicating ink and ribbon mucilage business to George Bliss and Charles Holland, who had acquired foreign rights a month earlier. |
| 5 June | Loses a patent interference case on acoustic multiple telegraphy to Elisha Gray. |
| c. 6 June | Designs combination telephone transmitter–electromotograph receiver. |
| c. 8 June | Tests sextuplex system on Western Union line from New York to Boston after extensive experiments in laboratory and then abandons its development in early July. |
| 28 June | Quadruplex Case final arguments conclude. |
| 2 July | Samuel Edison leaves Menlo Park for Port Huron. |
| 3 July | Demonstrates embossing recorder/repeater to Western Union officials and British telegraph officials William Preece and Henry Fischer. |
| 17 July | Conceives telephone message recorder/repeater. |
| 18 July | Conceives phonograph. |
| 19 July | Edward Johnson and George Barker exhibit Edison's musical telephone before large crowd at the Permanent Exhibition Hall in Philadelphia. |
| 19 July? | Finishes preparing preliminary specification for British telephone patent, which includes description of phonograph. |
| 21 July | Visited at Menlo Park laboratory by scientists George Barker and Henry Draper, and electrical manufacturer William Wallace. |
| 27 July | Visited at Menlo Park laboratory by Alexander Siemens, nephew of William Siemens. |
| 30 July | Begins to develop carbon "fluff" for telephone transmitters. |
| 1 August | Edward Johnson gives second telephone exhibition concert in Philadelphia and then begins a series of concerts along the eastern seaboard that continues through the end of the year. |
| 3 August | Begins month-long correspondence with Henry Draper regarding spectroscopy. |
| 4–10 August | Conducts telephone experiments with Thomas David at Menlo Park laboratory and over a line in lower Manhattan. |
| c. 7 August | Sends Charles Edison to Port Huron to represent his interest in street railways. |
| 10 August | Exhibits combination transmitter–electromotograph receivers built by Joseph Murray to Western Union officials and begins telephone line tests in New York City. |
| Mid-August | Tests various telephone designs over lines in New York City. |
| 20 August | Demonstrates a new telephone design to William Orton and other Western Union officials. |
| 21 August | Western Union announces agreement to purchase control of Atlantic and Pacific, thus ending commercial and legal conflicts between the corporations. |
| 24 August | Begins designing hand-held telephones. |
| Begins using newly installed gas lighting machine at laboratory. | |
| 25 August | Visited at Menlo Park by Robert Watson of Montreal, who wants to introduce Edison's telephone in Canada. |
| 9 September | Resigns his position as Atlantic and Pacific electrician. |
| Conducts experiments with electric arc lights. | |
| 10 September | Files depositions by himself, Batchelor, and Adams in electric pen patent interference case against Henry Trueman and gives evidence in hand-stamp patent interference with A. E. Hix. |
| c. 10 September | Conducts first experiments with incandescent electric lighting. |
| 11–13 September | With laboratory staff goes fishing in Raritan Bay. |
| 15 September | Signs an agreement with Franklin Badger, associate of Robert Watson, regarding the marketing of his telephone in Canada. |
| 17 September | Demonstrates a new transmitter to William Orton, who orders 150 sets of transmitters and receivers for Western Union subsidiary Gold and Stock. |
| 18 September | Proposes to George Bliss that Bliss and Charles Holland sell rights to European telephone patents. |
| With George Prescott signs agreement with Stephen Field and Cornelius Herz regarding European quadruplex patents. | |
| 28 September | Learns of successful quadruplex telegraph tests conducted on British Post Office lines by Gerritt Smith and George Hamilton. |
| 29 September | Learns first telephone patent application will be suspended pending resolution of patent interference conflicts. |
| 5–8 October | Redesigns telephone transmitter being manufactured by Joseph Murray. |
| 6 October | Wins electric pen patent interference against Henry Trueman. |
| 18 October | Participates in Edward Johnson's telephone exhibition at Jersey City. |
| 22 October | Begins using disks of a plumbago-rubber mixture in place of fluff in telephone transmitter. |
| 26 October | Begins using disks of lampblack and rubber in telephone transmitter. |
| 17 November | Western Union establishes the American Speaking Telephone Co. to combine its interest in Edison's telephone patents with the Harmonic Telegraph Co.'s ownership of Elisha Gray's patents. |
| Mid-November | Devises induction-coil circuit for telephone. |
| November | Explores alternative, noncarbon transmitter designs. |
| 1–3 December | Tests induction-coil circuit for telephone. |
| 1–6 December | John Kruesi makes first tin-foil, cylinder phonograph. |
| 7 December | Demonstrates his cylinder phonograph at Scientific American office in New York. |
| 12 December | Wins electric pen patent interference against Edward Stewart. |
| 15 December | Executes first phonograph patent application. |
| 16 December | Receives old "Telegraphy" entry for Appleton's Cyclopedia of Applied Mechanics, which he has been commissioned to revise. |
| 17 December | Signs agreements with George Bliss and Hungarian Count Theodore Puskas regarding the sale and exploitation of his European telephone and phonograph patents. |
| Dec 26 | Experiments with phonograph recording played over telephone to New Brunswick, N.J. |
| 27 December | Confers at Menlo Park with Edward Johnson, Uriah Painter, and Gardiner Hubbard about their proposals that he break his contract with Western Union and let them form a company to market his phonograph. |
| c. 29 December | Proposed as a scientific member of the American commission to the 1878 Paris Universal Exposition. |
| 31 December | Demonstrates phonograph to William Orton. |