286 
Scientific Notes. 
[April, 
rents from doubtful sources of eledtricity, and it is excellent as a means of 
testing leaky insulators. Among the fadts already proved by the telephone 
may be mentioned the existence of currents due to induction in wires conti- 
guous to wires carrying currents, even when these are near each other for 
only a short distance. Mr. Preece finds that if the telephone wire be enclosed 
in a conducting sheath which is in connection with the earth, all effects of 
eleCtric induction are avoided ; and, further, if the sheath be of iron, mag- 
netic induction also is avoided, and the telephone aCts perfectly. It appears 
that conversation can be carried on through ioo miles of submarine cable, or 
200 miles of a single wire, without difficulty, with the instrument as now 
constructed ; but the leakage occurring on pole-lines is fatal to its use in wet 
weather for distances beyond 5 miles. 
M. Demoget, of Nantes, has experimented with two Bell telephones in an 
open field. He held one of these to his ear, while his son at a distance kept 
repeating the same syllable with the same intensity of voice into the second 
instrument. He compared in this way the sound heard from the telephone 
with that heard from the speaker, and calculated their relative intensities 
from the relative distances of their sources. From the results M. Demoget 
concludes that the telephone as a machine leaves much to be desired, since it 
can only transmit i-i8ooth of the original work. 
Dr. R. M. Ferguson has contributed some valuable “ Notes on the Tele- 
phone ” to the Royal Scottish Society of Arts. He takes exception to the 
vibration theory of Bell, viz., that it is the vibrations of the disk to and from 
the pole of the magnet, in excursions proportionate to the intensity, pitch, 
and quality of the vocal sounds, that electrically affeCt the instrument. He 
submits that at the receiving station it can be proved well nigh to demonstra- 
tion that it is a molecular tremor or vibration, and not a vibration mechanic- 
ally produced, that emits the sound ; and that this molecular vibration 
becomes louder the easier the sounding body vibrates. Seeing that there is 
the most perfect correspondence between the sending and receiving instru- 
ments, there is, he says, every reason to believe that the sending instrument 
exhibits the converse aCtion to the receiving instrument, and that there again 
sound aCts on iron so as to produce molecular changes, the eleCtric power of 
which is much enhanced by the vibration of the sounding body. 
The Molecular Theory of the Telephone has also been the subject of a 
paper at the King’s College Engineering Society, by Mr. C. W. Cunnington, 
who considers that the vibration of the iron disk of the sending instrument 
under the influence of sound is amply sufficient to induce currents of electri- 
city strong enough to cause the plate of the receiving instrument to vibrate, 
and thus to reproduce sound : he also referred some of the sound produced in 
the receiving instrument to the effeCt of the undulatory currents on the mag- 
net itself, thus explaining results obtained without the use of a vibrating disk. 
In comparing the vibrating disk of the telephone with the membrana tympani 
of the ear, Mr. Cunnington pointed out the faCt that the predominance of the 
fundamental note of a flat plate would drown a large number of the over- 
tones of the voice, thus causing many of the observed peculiarities of the 
sound transmitted in ordinary telephones ; the membrana tympani being 
funnel-shaped, whilst peculiarly susceptible to the influence of sound, had no 
fundamental note of its own, and therefore transmitted all of the sound vibra- 
tions impinging upon it (within certain limits) without giving undue prepon- 
derance to any particular note. 
The Count du Moncel finds that the vibratory plate of the recipient cannot 
merely be replaced by a very thick and massive armature without affecting the 
transmission of speech, but these vibratory plates may be formed of non- 
magnetic substances. The vibratory plate may even be totally suppressed 
without hindering the telephonic transmission provided the polar extremity of 
the magnet is placed close to the ear. Hence the vibrations which reproduce 
speech in the receiving telephone are principally produced by the metallic 
nucleus infolded by the coil. The vibratory plate serves merely to readt for 
the production of induced currents, when set in vibration by the voice, and 
by its readtion upon the polar extremity of the magnetic rod to reinforce the 
magnetic effedts produced by the latter. 
