To change from transmitting to receiving nothing is needed but the detachment of this wire from the Ruhmkorff coil terminal and its insertion through the aperture of the enclosing box so as to touch the coherer circuit. The object of the box is, of course, the protection of the coherer from undesired disturbances, exactly as described on [page 34], and the collecting wire has the function there described likewise.
The electric tapper-back is also mentioned on [page 31], but not as being operated through a relay by the coherer circuit’s own current. This last improvement seems to have been devised and employed by Prof. Popoff at Cronstadt in 1895 ([see Fig. 42]). No doubt it was arrived at independently again by Mr. Marconi and the telegraph officials who assisted him in his early experiments in this country.
The other box shown in [Fig. 51] is probably a stand-by in case of accident.
It is difficult to imagine a simpler contrivance, and it appeared to work at Dover dependably, the messages coming out slowly in ordinary dots and dashes, the torrent of sparks being sufficiently rapid not to necessitate the breaking up of the dash into a series of dots. The sluggishness of the Morse instrument or the relay, or the circuit as a whole, enabled this excellent result to be attained with apparent ease.
Fig. 51
(p. 761, The Electrician, Vol. XLIII.).—
Apparatus for Sending and Receiving, shown by Prof. Fleming to the British Association at Dover.
A diagram of Marconi’s connection of sensitive tube to the relay and tapper-back and Morse instrument, where W represents the elevated wire, is given in [Fig. 52].
Fig. 52
(Fig. 2, of p. 691, The Electrician, Vol. XLII.).—