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POPULAR SCIENCE REVIEW. 
emitted by tbe resonant box, corresponding with that of the vibrating fork 
at the transmitting station. A mere accident suggested in the first instance 
this remarkable form of apparatus, and the theory of its action still remains 
extremely obscure. 
Whilst English and American electricians have thus been busying them- 
selves with the telephone, the subject has by no means been neglected on 
the Continent. Thus M. Paul de la Cour, of the Meteorological Institute 
at Copenhagen, has constructed several forms of telephone, which have 
been successfully worked on some of the Danish lines. A tuning-fork is 
placed in a horizontal position, with its shank connected by means of a sig- 
nalling key with the transmitting battery. On vibration of the fork, one 
leg comes in contact with a metallic spring, whereby connection is mo- 
mentarily established with the line-wire. By rapidly making and breaking 
contact, a series of intermittent currents will be transmitted to the receiving 
instrument. This consists of a soft iron tuning-fork with each leg sur- 
rounded by a helix of silk-covered copper wire. On the passage of a current 
through the bobbins, the enclosed legs are magnetized. But in front of the 
legs are two electro-magnets, round which the current is also caused to cir- 
culate ; and as it is so arranged that the legs acquire opposite polarity, 
attraction ensues, and the legs are consequently pulled out each time the 
current passes. The rapid movements thus produced by intermittent cur- 
rents throw the surrounding air into vibration, and produce a note of the 
same pitch as that of the oscillating fork at the transmitting end of the 
line. If several instruments are employed, a number of distinct signals may 
be simultaneously transmitted along a single wire ; for the intermittent 
current acts only on the particular fork which is in unison with that at the 
other end, and which is therefore competent to take up the vibrations. 
As the telephone promises to become of great practical value, it is interest- 
ing to look back upon the earliest form of the instrument, and mark its 
relation to the later forms of apparatus. There can be no doubt that the 
oldest telephone is that which was invented in 1861 by Professor Reiss, of 
Friedrichsdorf, near Homburg. This is in fact the parent of all the recent 
telephonic brood. In using Reiss’s instrument the operator sings through a 
mouthpiece into a wooden box, and thus throws into vibration a thin mem- 
brane, which is stretched across a large aperture in one side of the box. 
The membrane carries a small metallic disc connected with a battery, and 
every time this disc oscillates it comes in contact with a little platinum 
point attached to the wire of the telegraphic line. Contact is thus fre- 
quently made and broken, and a rapid succession of currents is consequently 
transmitted. The currents circulate around the helix of an electro-magnet 
at the receiving station, where they magnetize and demagnetize the en- 
closed bar more or less rapidly, according to the character of the note. But 
this rapid magnetization and demagnetization give rise to molecular changes 
in the bar, which produce a musical note : it is in fact the “ galvanic music ” 
which Page discovered in America forty years ago, but which remained un- 
utilized until Professor Reiss suggested this application. 
Although Reiss is fairly entitled to be called the inventor of the tele- 
phone, it is worth noting, as an historical curiosity, that the invention had 
been anticipated several years earlier. Dr. Paget Higgs has lately written to 
