530 Intelligence and Miscellaneous Articles. 



The difference in the rates of propagation and decay of waves of 

 high and low frequency doubtless constitutes the limitations to 

 the use of the telephone. As"the several harmonic components of 

 a complex tone advance along a conductor, they keep shifting their 

 relative phases according to the difference in their rates of propa- 

 gation and also change their relative intensities according to the 

 difference in their rates of decay, thus changing the resultant 

 combination tone ai d materially altering its quality. These effects 

 are always present in circuits containing distributed static capacity 

 but are not so marked when there is no self-induction. — Sillimaris 

 Journal, November 1892. 



Physical Laboratory of Cornell University, 

 July 1892. 



EXPERIMENTS ON THE CONDUCTIVITY OF INSULATING BODIES. 

 BY M. EDOUARD BRANLY, M.D. 



Insulating bodies in a very thin layer seem apt to become 

 conducting, and their conductivity presents some peculiar characters, 

 an idea of which is given by the following experiment. 



Forin a circuit containing a Daniell cell, an ordinary galvano- 

 meter, and fine metallic filings contained in a tube of glass or 

 ebonite, between two metallic rods acting as electrodes. The 

 file-dust opposes to the current of the Daniell cell an enormous 

 resistance, often over ten million ohms, so that the needle of the 

 galvanometer remains in equilibrium at zero. 



The thing being thus, if one produces in that circuit a sudden 

 displacement of electricity at high potential, whether by exciting 

 at a distance a spark of a Leyden jar, or simply by putting for a 

 few moments a point of the circuit in contact with one of the 

 poles of a battery of one or two hundred cells, the file-dust will 

 easily convey the current of the Daniell cell ; its resistance is 

 lowered to some hundred ohms or even less, and such conductivity 

 persists during many hours, or even many days. It is immediately 

 and completely suppressed by a very slight shock on the tube 

 containing the filings. 



In order to show that the shock has not suppressed the con- 

 ductivity by a modification in the relative positions of the molecules, 

 one may take instead of the tube with metallic filings another tube 

 containing a carefully made mixture of resin and metallic dust, 

 in proper proportions, amalgamated at the temperature of fusion 

 of the resin. 



Such a mixture, pasty when hot, becomes solid and extremely 

 hard when cold. Such a tube, which presents an infinite resistance 

 to the current of a single Daniell cell, becomes conducting under 

 the same circumstances as the metallic dust with intervals of air ; 

 and its conductivity disappears also under a slight shock. You may 

 thus reproduce and suppress it alternately as often as you wish. 



These experiments may be diversified in a great number of 

 ways. — Comptes rendus de VAcademie des Sciences, 24 Nov. 1890 

 and 12 Jan. 1891 ; Bulletin de la SocietS internationale dlelectriciens, 

 no. 78, May 1891. Communicated by the Author. 



