Current loith a Magneto-Teleplione Transmitter. 303 



strength of tlie current produced by a magneto-transmitter 

 under varying conditions of magnetization, and of the mag- 

 nitude of the momentary changes in the magnetic condition 

 of the core of the receiving-telephone when subjected to the 

 action of undulatory or other brief currents, as influenced by 

 the strength of the primitive permanent magnetization of the 

 core. The present paper contains only the results of a series 

 of experiments relating to the first of these ; that is, to the 

 eflFect of varying strength in the magnet of the transmitter, 

 the study of the allied problem of the receiver being still in 

 progress. 



The apparatus employed consisted of a cylindrical bar of 

 soft iron, about 4^ inches in length and \ of an inch in dia- 

 meter, around one end of which was placed a coil of fine wire 

 similar to that used in ordinary telephonic practice. The 

 resistance of this coil was 100 ohms. It was placed in circuit 

 with a balHstic mirror-galvanometer, from whose deflexion 

 the momentary current produced in the coil by any variation 

 in the strength of the core could be determined. The dia- 

 phragm, which was in all cases 2^^ inches in diameter, was in 

 its usual place o'pposite the end of the magnet about which 

 the wire coil was w^ound, and about j^q of an inch from that 

 end. By means of a rod carrying a cam moved by a weight, 

 a rapid inward push of definite amount was given to the dia- 

 phragm, thereby inducing a current in the coil already referred 

 to, and so deflecting the needle of the ballistic galvanometer. 

 The soft iron bar was also surrounded by a second helix, 

 through which was passed a current from a storage battery, 

 serving to magnetize the core. A tangent-galvanometer 

 inserted in this circuit gave the strength of the magnetizing 

 current. A magnetometer placed in tbe prolongation of the 

 axis of the core, which last occupied an east and west position, 

 made known the relative strengths of the field produced by 

 the core under dift'erent conditions of magnetization. 



Corresponding observations of the magnetometer-reading, 

 and of the current induced when the diaphragm w^as moved 

 by the cam, were made throughout a widely varying range of 

 strength of field, and the results were represented graphically 

 by constructing a series of curves in which ordinates represent 

 the relative strength of field, and abscissas the current due to 

 a given predetermined throw of the diaphragm (about y^^^y of 

 an inch), as ascertained from the readings of the ballistic 

 galvanometer. 



One of these curves is shown at 1, fig. 1, the core in this 

 case being a cylindrical bar of Norway iron 4^ inches long 



