May II, 1876] 



NATURE 



31 



The sending reed is ingeniously maintained in constant 

 vibration by a pair of intermittent electro-magnets which 

 are magnetised and demagnetised by the vibrating reed 

 itself. 



Thus in Fig, i (which represents the transmitting part 

 of the telephone and its connections for a single note), 

 the current from the magnet battery flowing in the direc- 

 tion of the small arrow passes through the pair of electro- 

 magnets A to the terminal r of the reed R, and thence by 



the spring contact b and the wire bz to the battery again, 

 completing its circuit without passing through the other 

 pair of electro-magnets B, which are not therefore mag- 

 netised. The reed R is consequently pulled over by the 

 electro-magnets A. But on this taking place the spring 

 contact b is broken and the circuit is no longer com- 

 pleted through bz but through the electro- magnets B, 

 which are consequently magnetised, and tend by their 

 induction on the reed to neutralise that of B. The reed 



( SENDING 

 UEY OR •( INSTRUMENT 



^^=0 



A 



MAGNET 

 BATTERY 



RECEIVING 

 INSTRUMENT 



EARTH 



Fig. I. 



therefore springs back to its intermediary position, but in 

 so doing the contact at b is again made and the electro- 

 magnets B again short-circuited and the reed pulled over 

 (or rather assisted over, for it has its own resilience or 

 spring) towards A ; so this goes on keeping the reed in 

 vibration between the electro-magnets and alternately 

 making and breaking the spring contact b and also that 

 of a, the number of contacts per second being dependant 

 on the vibrating period of the reed. 



t; While this is going on the reed of course emits its mu- 

 sical note. Two Leclanche or bichromate cells are 

 sufficient to work the transmitter and give a good note. 



TO EARTH 



^^^ 



Fig. 2. 



The spring contact b is to be adjusted by the screw there 

 seen until the note emitted by the reed is both loud and 

 pure. The magnets A and B are adjustable to or from the 

 reed by the milled heads C and D. 



The spring contact a just mentioned belongs properly 

 to the line circuit. It is the intermittent contact which 

 interrupts the current sent into the line. As will be seen 

 from the diagram the circuit of the sending battery is 

 made through the key K, the reed, and the spring contact 

 a. On holding down the key K the current flows into the 

 line, being interrupted, however, by the contact a as 

 many times per second as the reed vibrates, and this 

 intermittent current flowing to earth at the distant station, 



s made to elicit a corresponding note from the receiving 

 apparatus there. 



The receiving instruments are of two kinds, electro- 

 magnetic and physiological. 



In the first there is a plain double electro-magnet with 

 a steel tongue having one end rigidly fixed to one pole, 

 the other end being free to vibrate under the other pole. 

 This stands over a wooden pipe closed at one end. 

 Thus in Fig. 2 / T is the steel tongue fixed at / and free at 



EARTH* — «^ 



4^ LINE 



Fig. 3. 



T, while P is the sounding-pipe. The received current, 

 coming from the line and passing through the electro- 

 magnet M to earth, sets the tongue vibrating, and the 

 pipe gives forth the same note as the reed at the sending 

 I station. Ten Daniell cells working through 1,000 ohms, 

 I give a good strong note, especially when the receiver is 



