These three letters to Robert H. Thurston, engineer and director of Sibley College at Cornell University, are from January 1888, July 1889, and December 1893. The 1888 letter is an invitation from Edison to visit his newly constructed laboratory in West Orange. The 1889 item is a letter of introduction by Edison for Martin J. Insull, brother of his former secretary Samuel Insull. The 1893 letter is by Arthur E. Kennelly, Edison's chief electrical assistant, and pertains to a lecture on "Submarine Telegraph Engineering" that he wished to give at Sibley College.
An online finding aid to the archival collection is available.
[X008BA], Letter from Thomas Alva Edison to Robert Henry Thurston, January 18th, 1888 1888-01-18
[X008BB], Letter from Thomas Alva Edison to Robert Henry Thurston, July 6th, 1889 1889-07-06
[X008BC], Letter from Arthur Edwin Kennelly to Robert Henry Thurston, December 29th, 1893 1893-12-29