4 8 2 D O C . 6 7 O P I N I O N O N A T L A S V S . S I G N A L
Deutsches Reichspatent 99667, entitled “Schallweiser mit zwei akustischen Empfängern,” was
granted on 18 October 1898 to David P. Heap.
US Patent 224199, entitled “Topophone,” was filed on 30 September 1879 on behalf of Alfred
M. Mayer. Deutsches Reichspatent 93144, entitled “Apparat zur Bestimmung der Herkunftsrichtung
eines Schalles,” was granted on 10 August 1897 to E. Hardy. Both devices work as follows: sound
signals arriving from two microphones are made to interfere with each other by connecting two sound
conducting tubes; the resultant signal is transmitted to the ears of the observer, who can hear the inter-
ference while the setup is being rotated.
Mayer claims that the novelty of his patent consists of “[t]he combination of two resonators or
soundreceivers and a single pipe with conducting or confluent tubes, connecting the resonators or
soundreceivers with the pipe, one or both of which conducting tubes are longitudinally adjustable,
substantially as and for the purposes set forth”; Claim 4 of US Patent 224199.