XLI._ON THE SUPPRESSION OF INDUCTION CLAMOUR 
IN TELEPHONES, sy W. F. BARRETT, r.rs.n, 
[Read June 16th, 1879.] 
THE main obstacle to the wide use of Telephonic communi- 
cation is the disturbance caused by the induction from neigh- 
bouring wives through which powerful currents are passing. 
This, as is well known, gives rise to a crackling sound, which 
becomes a tumultuous uproar when the induction is very powerful. 
The feeble Telephonic currents are completely swamped by the 
intrusion of a more powerful foreign element, and Telephonic 
communication becomes either difficult or impossible. 
Hence, to suppress the induction disturbance becomes a problem 
of high practical interest. Moreover, not only is Telephonic 
communication subject to this evil, but some of the more delicate 
Telegraphic arrangements now in use are seriously crippled from 
the same cause. Before referring to my own experiments, it is 
necessary briefly to explain the nature of this induction. 
Induction disturbances are of two kinds, either electro-static 
or electro-dynamic. In the former the conducting wire, the non- 
conducting air, and the neighbouring wires together, resemble a 
Leyden jar, or condensing arrangement. In the latter, or electro- 
dynamic induction, the juxtaposition of two or more wires having 
closed circuits, through one of which a current is flowing, re- 
sembles an ordinary induction coil, and it is the secondary 
currents set up in the Telephonic line by the strong currents 
employed in telegraphy on the other line, which is the chief cause 
of Telephonic disturbance. 
Tf the conductor be coiled on itself “extra” currents come into 
play, which increase the induction disturbance, so that “ whilst 
it is possible to speak through a cable 100 miles long straight in 
the sea, it is impossible to speak through 20 miles when coiled in 
a tank.”* 
* Preece. Proc. Physical Society, January, 1878. 
Scien. Proc.,R.D.S. Vou, 11, Pr. 1v. ee, 
