TRANSACTIONS OF THE SECTIONS. 37 



brought to bear upon it. Starting from Reiss's 



transmitter he simply substitutes for the platinum 



point (d) asmall cylinder of plumbago, and he finds 



that the resistance of this cylinder varies sulli- 



ciently with the pressure of the vibration of the 



diaphragm to cause the currents transmitted by 



it to vary in form and strength to reproduce all 



the varieties of the human voice. His receiver 



also is novel and peculiar. In 1874 he discovered 



that the friction between a platinum point and 



moist chemically prepared paper varied every timo 



a current passed between the two, so that the rate with which the paper moved was 



altered at will. Now by attaching to a resonator («) a spring (b), whose platinum 



face (c) rested on the chemically prepared paper (d), whenever the drum (c) was 



rotated and currents sent through the paper, the friction between c and e is so 



modified that vibrations are produced in the resonator (a), and these vibrations are 



an exact reproduction of those given out by the transmitter at the other station. 



Edison's telephone, though not in practical use in America, is under trial. In 

 some experiments made with it, songs- and words were distinctly heard through 

 12,000 ohms, equal to the distance of 1000 miles of wire. 

 ^ Bell's telephone is, however, in practical use in Boston, Providence, and New 

 York. There are several private lines that use it in Boston, and several more are 

 under construction. I tried two of them, and though we succeeded in conversing, 

 the result was not so satisfactory as experiments led one to anticipate. The inter- 

 ferences of working wires will seriously retard the employment of this apparatus ; 

 but there is no doubt that scientific inquiry and patient sidll will rapidly eliminate 

 all practical defects. 



To Professor Graham Bell must be accorded the full credit of being the first to 

 transmit the hiiman voice to distances beyond the reach of the ear and the eye by 

 means of electric currents. 



On an improved Lantern Galvanoscope. By S. P. Thompson. 



With the view of making the movements of a galvonometer needle visible to 

 large audiences, this instrument is constructed as a lantern-slide. The galvanometer, 

 iu which the needle- turns upon a horizontal axis, resembles in miniature that of 

 Becquerel. The scale behind the index is transparent in order that it may be pro- 

 jected u|jon the screen. 



■ 



On the Effect of Transverse Stress on the Magnetic Susceptibility of Iron. 

 By Sir W. Thomson, F.B.S. 



On the Determination of Temperature-coefficients for insulating Envelopes. 

 By T. T. P. Betice Wabeen. 



Sound. 



On a new Method of Determining the Vibration-number of Tuninq^Forhs. 



By Prof. H. M'Leod. 



On Binaural Audition. By Silvanus P. Thompson, B.Sc, B.A. 

 Two tuning-forks tuned nearly in unison when sounded together give rise to inter- 



