284 Scientific Proceedings, Royal Dublin Society. 
ing the primary circuit of any telegraphic transmitter an induced 
wave is generated in the adjoining line opposite in direction to 
the primary; at the moment of opening the primary circuit, an 
induced wave moving in the same direction as the primary is 
started. In the magneto-telephone, it is true, alternating cur- 
rents are transmitted, but in the carbon telephone and its con- 
geners the currents are in one direction. This difference in 
character between the induced and certain telephonic currents 
presents, therefore, one mode of attacking the subject. I have 
not, however, done anything in this direction, though it is con- 
ceivable the telephone receiver may be made to respond only to 
currents in one direction, and hence much of the induction clam- 
our could then be suppressed. Again (b.), a difference may exist 
between the electric potential of the induced and that of the 
telephonic current, and (c.) as Mr. Fitzgerald, F.7.¢.D., has sug- 
gested to me,a notable difference exists between the period of the 
two classes of electric waves. .The waves induced by telegraphic 
currents are of comparatively long duration, whereas the tele- 
phonic waves are of extremely short duration. 
These two considerations, b and ¢, led me to make the following 
experiments, Jirst,as regards the possible elimination of the 
induced currents through any sensible difference of potential. 
For this purpose the line wire was led through a sort of lightning 
discharging arrangement connected with the earth, whereby, if 
the potential of the induced currents were sensibly great, it was 
hoped that some of the disturbance would be got rid of. A group 
of some hundred fine needle points was fixed to the line wire, and 
these were surrounded by another group of needle points closely 
juxtaposed, but not touching, the outer group being joined to 
earth. But though the points were brought close to each other 
no beneficial effect was noticed. 
The arrangement was then enclosed in a wide glass tube, which 
could be exhausted, as shown in Fig. 7, but even at a high rare- 
faction no sensible diminution of the disturbance was noticed. 
