Fig. 44 shows the simplest form of its connection to a one-cell battery A and a polarised relay B, which switches on another battery of several cells _a_ operating the Morse instrument or electric bell or sounder _b_ and also the tapper-back _c_, the hammer of which raps gently on the coherer tube at every signal. [Illustration: FIG. 44 (Fig. 8 of Slaby’s book).--Slaby’s arrangement of Coherer and of tapper-back and relay connections.] The actual apparatus is depicted in two views, Figs. 45 and 46, where will be recognised on the left-hand side the coherer and tapper-back; in the middle the batteries, both for relay and for coherer circuits; and on the right-hand side a relay and the signalling or calling instrument, in this case shown as an ordinary electric bell. [Illustration: FIG. 45 (Fig. 16 of Slaby’s book).--View of Slaby’s Receiving Apparatus, with call-bell rung by relay, or with Morse instrument joined on to terminals _M_, and switch to change from Calling to Signalling. _K K_ are the terminals of elevated wire and earth, and the Coherer and Tapper-back are close to them.] [Illustration: FIG. 46 (Fig. 17 of Prof. Slaby’s book).--An elevation view of Prof. Slaby’s same Apparatus, showing the electromagnet and hammer of the tapper-back worked by relay current from local battery, as in Popoff’s plan of 1895.] A Morse instrument is to be connected to the terminals M, and either it or the bell can be switched into the circuit at pleasure. The form of relay depicted is special to Slaby, but the rest of the arrangements are practically identical with those shown by Marconi at Dover. Fig. 47 gives a diagram of the actual connections. Fig. 48 is a picture of one of Slaby’s signalling stations, showing the way the elevated wire enters the building. [Illustration: FIG. 47 (Fig. 19 of “Spark Telegraphy”).--Diagram of Slaby’s connections in the above apparatus. F is the coherer and K the tapper-back.]