Engel, Friedrich Karl, ed. (2006) "Oberlin Smith and the invention of magnetic sound recording: An appreciation on the 150th anniversary of the inventor's birth". Smith's caveat of 4 October 1878 regarding the recording of sound on magnetic media appears on pp. 14–16. Available at: RichardHess.comArchived 21 October 2006 at the Wayback Machine
Engel, Friedrich Karl, ed. (2006) "Oberlin Smith and the invention of magnetic sound recording: An appreciation on the 150th anniversary of the inventor's birth". Smith's caveat of 4 October 1878 regarding the recording of sound on magnetic media appears on pp. 14–16. Available at: RichardHess.comArchived 21 October 2006 at the Wayback Machine