Electrical World, December 8, 1906, page 1121:
Wireless Telephony--RUHMER--As was recently noticed in the Digest, Poulsen has succeeded in producing undamped electric oscillations for wireless telegraphy; the present author says this makes wireless telephony at once possible. Like Poulsen he uses a direct-current arc lamp in a hydrogen atmosphere. Fig. 4 shows the arrangement of the transmitter. In his first experiments a b was not used as vertical wire, but was in the form of a closed circuit containing a brush-light oscillograph tube. By speaking into the microphone, M, a corresponding picture of the sound vibrations was obtained by means of a rotating mirror from the oscillograph tube. To use this arrangement as a transmitter for wireless telephony, it is only necessary to arrange a b in the form of a vertical wire as shown in the illustration. The receiver is shown in Fig. 7, where S is an electrolytic wave-detector, T a telephone. The author has so far made experiments only in the laboratory, with vertical wires a b of about 1.5 meter length. He was able to transmit speech over a distance of 30 meters very clearly.--Elektrotechnische Zeitschrift, November 15.