632 Proceedings of the Hoy at Society 
portion to the conductivity of each. If it now he accepted that the 
sounding action be like heat proportionate to the square of the 
current strength, the apparent discrepancy is accounted for. Suppose 
the conductivity of silver to be ten times greater than that of German 
silver, then in the silver plate a tenfold greater current would be 
induced, and would have in consequence one hundredfold greater 
sounding power than that of the German silver in the same resistance : 
but as the resistance of the German silver is ten times greater than 
that of the silver, there would still be a tenfold louder sound in the 
silver than in the German silver, quite a sufficient margin to remove 
the discrepancy. In addition to the action within the plates here 
discussed, there may of course also be the external push-and-pull, 
as with the iron disc. In wires the length involved has little 
effect on the sound ; for though a long stretch of wire does 
sound louder than a short one, the difference is by no means in 
keeping with the respective lengths. In thick wires no sound is 
got. I tried in vain with the strongest current I could conveniently 
use to get a sound out of a No. 14 copper wire. 
Now here at least it will be admitted that we have a molecular 
action. It may be replied that the earth’s magnetism has something 
to do with it. To show that it has not, we may try the somewhat 
inelegant feat of holding the end of the thin iron wire in the teeth, 
and turning it in every possible direction, when we shall find that 
the loudness of the ticking has no relation to direction. Again, 
when the string of the telephone is tied to the wire and made to go 
round it in a circle, we shall find no maximum or minimum points. 
This then is a telephonic action absolutely free from external push 
and pull, proceeding undoubtedly from molecular disturbance in the 
wire. That the action is magnetic in some way is evident from the 
exceptional position of iron in the series of metals. De la Eive held 
that the sounding action of an iron wire, when the seat of a dis- 
continuous current was almost identical with, and must be traceable 
to the same ultimate cause as, that it displays when placed in a 
magnetising helix excited by a similar current. The parallelism 
between the wire telephone and the ordinary electric telephone 
is so striking that no theory of the latter can be held to be 
complete without it includes the former. It seems to suggest that 
the sounds we hear in plates and rods under sudden electric or 
