308 



THE TELEPHONOGRAPH. 



an arm mounted on the left side of the frame strikes the tiny lever 

 shown in the illustration, raising the mag-net, and causing it to run 

 rapidly back to the beginning again (the carrier being guided b}^ the 

 coarse threaded shaft, shown parallel to the supporting shaft) this 

 operation taking but five seconds. The legs of this magnet are about 

 seven-sixteenth inch long, and are wound with bobbins of wire of 

 about the same size as those emplo^^ed on an ordinary receiving tele- 

 phone magnet. A cross section of the magnet is shown in fig. 2, let- 

 ter C. It has been found that a horseshoe form of magnet, as shown 

 in fig. 2, letter B, will not respond rapidly enough, and it is preferable 

 to employ two separate magnets electrical l_y connected, as shown in 

 fig. 2, letter C. In the ribbon form of tolephonograph the horse- 

 shoe magnet shown in fig. 2, letter D, may be used, but even here 

 two magnets electricall}' connected are preferable. This recording 

 electro-magnet, which has a resistance of 100 ohms, is connected in 

 circuit with an ordinary carbon telephone transmitter, and a couple 

 of cells of ))atter3% and preferal)ly with an induction coil in the usual 

 manner. When the transmitter is spoken into, it acts as a ta]) vipon 



UAG^T roR PCCOftD/f^G O^STCCi mffr 



Cfioss srcTic/v OF t 



M^CTT roR RFCORDllfO OM STCtL /DBBOV. 



A B C 



Fig. 'J. — Telephoiiograph magnets. 



the batter}^ and causes currents of var3Mng strength, and in propor- 

 tion to the strength of the sound waves impinging upon the diaphragm, 

 to pass through the wire wound on the electro-magnet. Now as the 

 steel wire wound on the drum passes in front of and in contact with 

 the poles of the magnet, its var3dng magnetic field magnetizes trans- 

 versely the steel wire, and the "lines of force" are permanentlv 

 recorded therein. After the steel spiral has been filled, which opera- 

 tion takes about thirty-nine seconds at an ordinary speed of talk- 

 ing, and records 100 to 120 words, the tiny magnet is placed at the 

 point where the record first started, and in place of the transmitting 

 telephone with which it was connected a Bell receiving telephone is 

 attached. The cylinder or drum again revolves, and as the magnet- 

 ized steel wire passes before the poles of the electro-magnet it forms 

 a species of magneto-electric generator, giving out currents of electricity 

 of a strength and direction corresponding to the magnetization of the 

 steel wire, which correspondingl}" afi'ect the Bell telephone, and repro- 

 duce the sounds and words originally spoken with absolute fidelity. In 

 Edison's phonograph and its modifications, such as the graphophone, 

 gramophone, etc., a stylus is always emploj^ed to indent the surface of 



