This letterbook covers the period April-June 1884. Many of the letters are by Edison. There is also correspondence by Samuel Insull. Most of Edison's letters are in the hand of Alfred O. Tate, acting as Edison's secretary. Included is correspondence relating to the purchase of supplies and equipment and to the payment of overdue bills. There are also cost and profit estimates for central stations in New Brunswick, New Jersey; Niagara Falls and Roundout, New York and Buenos Aires, Argentina. In addition, there are some letters concerning Edison's health. Among the recipients are William S. Andrews, Armington & Sims, Spencer Borden, Thomas P. Conant, and Henry A. Rowland. The front cover is marked "Construction Dept No 6." and is stamped "T. A. Edison. Construction Dept., 65 Fifth Ave, New York." The spine is labeled "1884" and is stamped "Letters C D 6." The book contains 500 numbered pages and an index. Approximately 40 percent of the book has been selected.