278 Scientific Proceedings, Royal Dublin Socicty. 
Further, if a rod of iron be enclosed within the coil, still further 
disturbance is produced by the electro-magnetic action of the 
current. When a current of electricity passes ronnd the coil of 
an electro-magnet its first effect is to magnetize the iron core, 
but by this act a momentary counter-current 1s generated in the 
wire, the effect of which is to retard and weaken the primary 
current. When many electro-magnets are in circuit, as, for in- 
stance, the call bells in a long line, the opposing induced magueto- 
currents become a most serious obstacle, and when the electric 
impulses succeed each other with great rapidity, as is the case 
with telephonic communication, the electro-magnets in the circuit 
will either totally absorb or greatly diminish the strength of the 
swiftly recurring telephonic currents. To suppress or absorb this 
magneto-electric induction, a condenser consisting of alternate 
sheets of some insulating material and tinfoil is employed; this 
remedy is found to be completely effectual, and hence is in general 
use. 
The retarding effect of electro-static induction on submarine 
lines does not appear to interfere with Telephonic communication 
up to 100 miles. Between Guernsey and Dartmouth, 60 miles 
apart, conversation was easily carried on; so it was between 
Holyhead and Dublin, 67 miles. Beyond this, Mr. Preece, in the 
paper before quoted, states, that up to 150 miles it was like 
speaking through a respirator, and beyond 200 miles speaking 
could not be heard, though singing was heard through an artificial 
cable 3,000 miles long. 
Current induction is, however, more difficult to surmount. Mr. 
Wilson, of Chicago, was, | believe, the first to suggest a method 
of overcoming this defect, a necessary preliminary to the proper 
working of the quadruplex telegraph. The principle of Mr. 
Wilson’s plan was to establish, in the disturbed line, a counter 
current at the same moment and of the same strength and 
duration as that of the induced current generated on it by the 
changes of potential occuring in the neighbouring wire. His 
arrangement was as follows, Fig. 1 :—Two coils, P and S, from the 
disturbing line A and the disturbed line B, are so wound that 
currents are induced in them in a direction opposite to those 
occurring in the straight parts of the circuit. The coils P and S 
