PHYSICS. 255 



emy a form of telephone, in winch a plate of sheet-iron is ar- 

 ranged with the end of a black-lead pencil pressing lightly 

 on the central part. The plate and pencil are made part 

 of an ordinary telegraphic circuit, at the other end of which 

 is an ordinary telephone with a soft iron bar in the coil in- 

 stead of a magnet. A battery of two Leclanche cells only 

 is necessary. The plate, vibrated by the voice, compresses 

 the black-lead, and so causes variations in its resistance, 

 transmitting in this way a variable current to line. Da 

 Moncel said to the Academy that, if this was original with 

 the authors, it was entirely anticipated by the precisely sim- 

 ilar arrangement contrived by Edison more than two years 

 ago, and now practically utilized in his carbon telephone. 

 Only in this instrument a disk of carbon is used in place of 

 the pencil lead. 



Trouve has proposed a modification of the speaking tele- 

 phone by which he hopes to increase the loudness of the 

 tones received. He simply places several diaphragms about 

 a cavity, each diaphragm having its magnet and coil. When 

 one talks into the cavity, each membrane is thrown into vi- 

 bration, and each generates a separate current, which all 

 unite into one on the line, thus intensifying the sound. 

 Such telephones he proposes to utilize for repeating pur- 

 poses, since if half of the wires go on and the other half go 

 back, talking to the next station beyond a message just re- 

 ceived must send back to the previous station the message 

 which has just been received from it. 



Breguet has invented an exceedingly ingenious and novel 

 telephone based on an entirely ne.w principle. This is the 

 fact first observed by Draper, and thoroughly investigated 

 by Lippmann, that a close connection exists between capil- 

 larity and electricity, and that electric tension will change 

 the form of liquid meniscus, and changing by mechanical 

 means the form of the meniscus will develop an electric cur- 

 rent. In Breguet's apparatus the sender and receiver are 

 exactly similar. Each consists of a vessel containing mer- 

 cury with dilute acid above it, into which dips a tube con- 

 taining mercury, the lower end of which is drawn out to a 

 capillary point. On speaking into the top of one of these 

 tubes the sound waves depress the mercury, increase the 

 convexity of the meniscus, and generate an electric current, 



