Theobald Böhm’s comment on the open G sharp key

In 1981, 5 letters of Theobald Böhm to Wilhelm Popp appeared in Sweden by the aid of my research ad in a music journal, which are today in the Munich Municipal Archives, Estate Theobald Böhm I. In his letter of 5th February 1865, Theobald Böhm discussed in detail the open and closed G sharp key (original in German).