630 
Proceedings of the Royal Society 
as loud. A thin iron wire is therefore the most rudimentary form 
of a telephone. G-ott’s telephone has thus another explanation in 
addition to that of the mere twisting round in a magnetic field; 
for if only the coil he left without a field, or even if only one con- 
volution of it he left, and held in the chaps of a vice, its power of 
moving the paper disc would not wholly disappear. 
When the paper telephone was attached to the thin iron wire, and 
the distant break worked by the hand of an operator, a loud sound was 
heard when the dipper of the break entered the mercury, and another 
equally loud, hut not louder, when it was lifted out. In this case 
the break was two rooms off from the listener, at a distance of from 
30 to 40 feet, and when the operator was made to say “in,” “out,” at 
each motion, short as the distance was, the wire sounded before the 
voice. The sounds thus given had a clear metallic ring about them. 
This, however, disappeared when the wire was coiled tightly round 
the finger. The mechanical telephone enables us to hear such sounds 
in all portions of the wire without any interruption. We can hear, 
for instance, the half musical sound in a straight wire, the dull un- 
musical sound when the wire is tightly coiled, and the increase of 
this when several convolutions of a covered wire are kept tightly 
together. In the single wire, although the sound is loudest when it 
is tense, yet it is distinctly heard when perfectly loose. De la Eive 
tells ns that the resistance in the sounding wire must he greater 
than that of the remaining circuit, battery included. I have found 
that this is not necessary, for I can hear distinctly the sound of a 
thin iron wire when the current is the weak one furnished by a 
single Bunsen cell charged with water. The Bunsen cells mentioned 
here have an active medium surface of 40 square inches. Again, 
with a small magneto-electric machine for medical purposes, almost 
any experiment can he demonstrated. 
With reference to the strengths of current necessary to excite the 
wires, the characteristic of the telephone mentioned by Professor 
Tait, in his communication on the “ Strength of a Telephonic 
Current,” must he borne in mind, viz., that the telephonic effect 
does not depend so much on the actual strength of the sounding 
current as on the rapidity with which changes in the strength 
are effected. The break used in these experiments made from 
five to six interruptions in the second, that certainly was not very 
