Evening star., 1902-02-22

by pressing down the break-circuit key.
The latter is handled In the same manner
as the ordinary telegraph key. being kept
closed at short or long intervals as re-
qufred when using the dot and dash, or
Morse code.
"The simple apparatus just described is
now somewhat complicated by the addition
of a transformer and condenser, which
apparently have the effect OF intensifyfng
the spark and therefore increasing the
range Of perceptible signals. They in no
way. however. change the principle of the
transmitting messages.
The Receiving Station.
Let us now pass to the receiving sta
ton. The essential instrument Of the re-
ceiving apparatus is called coherer. 1t
consists of two metal plugs, or electrodes,
separated short distance from each other.
about one thirty-second of an inch. placed
in a glass tube or some other tube of in
sulating material. with the intervening
space partially filled with loose metal I'LL
ings. usually of steel, iron or nickel. 1t Is
also usual to have these filings semioxi-
died. This instrument was invented by
Branly, and not Marconi, popularity
supposed. The metal filings in the condi-
ton described do not afford sufhciently
good conductor to permit an ordinary vol
taic current to pass from one electrode TO
the other. When, however, a spark jumps
across this small interval in the coherer
the metal filings appear to arrange them-
selves In line from one eiectTOue " the
other sufficiently close to give good metallic
contact, and thereby complete the circuit
of local battery already connected to the
electrodes 1t is plain that this local bat
tery may be made to do certain work, such
as operating an ordinary sounder or re-
corder.
We must now establish a connection be-
tween the HertZian wave coming from the
distant station and the spark which passes
through the coherer, in order to establish
a practical working apparatus. Al the re-
ceiving station is an aerial wire, supported
as at the transmitting station; sometimes,
to multiply effect, number of aerial wires
are supported by masts, all of which
wires are brought together before connec-
ton is made to the instrument; sometimes
the length of the aerial wire is increased
to 400 or 800 feet by means OF balloon.
1T is natural to suppose that the effect
of the HertZian waves Will be increased
in proportion to the number OF conducting
surfaces impeding their progress. 1t ap-
pears that when the wave arrives 1t Gre
ates in the wire certain electric pulsa-
ton. current, or effect, which, passing in
to the operating room, Is led through the
primary Of an induction coil and then to
earth. 1t is curious fact that the wire
is more effective it, instead of being ex-
actly vertical, 1t inclineS to the vertical
somewhat less than 45 degrees. 1t will be
remembered that at the transmitting sta
ton the poles Of the secondary coil are
practically connected, one to the earth
and the other to the air. We now COM
plete the circuit; the electric wave passes
through the air, Is caught by the vertical
wire and goes to earth, doing certain work
en- route That work Is to excite the pri-
mary of an induction coil. which in turn,
excites the secondary winding OF the coil
connected directly to the electrodes of the
coherer. This produces the effect descr1b-
ed. The little break of one thirty second or
an inch is bridged over, the local battery
comes in play and the sounder or recorder
is brought into operation. There are GER
train transformers, cOndensers, ETC., used
to magnify this effect, which 1t Is not
necessary for US to discuss.
Use Of the Taper.
THE essential features Of the apparatus
have now been described, with one ex-
ception. We have changed our coherer
from a non-conducting instrument to one
which readily conducts the current Of the
local battery; 1t therefore is not in condi-
ton to repeat the work already described.
and 1t must be restored to its original
status before the arrival of another Hertz
ian wave can be signaled. In the same
circuit as the local battery Is what Is
known as Taper consisting Of ham
mer worked by an electromagnet, which
every time the circuit is closed gently taps
the coherer in the center; this tap causes
the metal filings to drop from the posi-
tions arranged by the spark to irregular
positions. thus breaking the circuit of the
local battery. Another wave comes along,
the act described Is repeated, and this Is
kept UP Indefinitely. The operator by
keeping his key down short and long In
tervals causes the receipt Of dots and
dashes, and thus the signification Of the
waves Is made complete