The Electrical experimenter

May, 1917 THE ELECTRICAL EXPERIMENTER 73
to give a most terrible shock, and proves a
most formidaljle antagonist when it has
grown to its lull Icngtli of five to six feet.
In the Silurus shown in our Fig. 10, the
electric current Hows from head to tail.
It has been shown by several scientists
that nerve excitations and muscular contractions
of human beings are the scat of
slight electrical currents, h'or one thing
it has been shown that the beating ol the
heart really creates rhythmical electro-motive
force.
Photo-Klicctricity: One of the most interesting
sources of electrical energy and
also one of the most direct methods of
production of electro-motive forces is found
in the f'hoti'-clrclric cell. Simply explained
this remarkable device comnrises nothing
more than two cupper plates, one of which
is perforated and lilackened by oxidizing
in a gas flame, while the rear or second
l)late is polislied, and both of which plates
are placed in a suitable tank containing a
salt-water solution. One side of the tank
which contains the coi)per plates is lifted
with a glass window and when sunlight,
or any other source of light, is allowed to
strike the cell, there is a difference of electric
potential set up between the front and
rear copper plates. This particular cell as
developed by Mr. Theodore VV. Case, was
described extensively in an article which
appeared in the September, 1916, number of
this journal. It was found possible with
some of these photo-electric cells to obtain
a voltage of one-tenth and an amperage of
two-tenths ; the cell delivering a steady
current as long as the light shown on it.
It is of course possible to connect a large
number of cells in series or parallel to obtain
any voltage or current desired.
Radium Electricity: It is generally conceded
in scientific circles that the activity
possest by radium is fundamentally electrical
in nature. Radium gives off three
kinds of rays known as the alpha, beta and
ya::niia rays. It is possible to influence two
of these rays (alpha and beta rays) by
means of a magnet or an electro-magnetic
field, which indicates that they are undoubtedly
electrical in their fundamental
structure. Another experiment, which any
schoolboy can readily perform with a piece
of radio-active mineral, is as follows : First,
an electric charge is produced on a sensitive
gold leaf electroscope, so that the leaves
diverge; then grasp a piece of the radioactive
mineral (some may be so fortunate
as to possess a tube containing a small
quantity of radium bromid) and bring tliis
into proximity with the metal ball or disc
at the top of a charged electroscope. It
will be noted that the latter loses its charge
on the gold leaves almost instantly ; ttu.
electronic activity of the radium bromid or
other radio-active substance used creating
a change in the electrical field about the
electroscope, apparently making it more
conductive, so that the bound electric charge
on the gold leaves can escape. Those interested
in the subject of "Radium" and
the many electrical and other effects created
by the greatest mystery of the scientific
world to-day will do well to read the
extensive article on this subject, which appeared
in the September, 1916, number of
The Ki.f.ctric.\l Fxperimexter. .
RADIO ENGINEERS DINE.
The Wasliington section of the Institute
of Radio iMiginecrs pave a dinner, March
third, at the Commercial Club, Washington.
D.C., complimentary to Urigadicr-gcneral
George O. Squier. chairman of the Washington
section. The following named gentlemen
from New York participated: R. A.
Weagant, chief engineer, and David Sarnoff,
commercial manager, of the Marconi
Wireless Tclegrapli Co., of America; Major
J. .Andrew White and W. J. Hernan, of
the Wireless Press.
THE IONIC RADIO SYSTEM AND
THEORY OF IONIC TUNING.
{Continued from page S')
detector and Weston relay are here connected
in multiple, the connections from
the local side of the Weston relay being
the same as above described.
The preferred type of my detector used
in this system is shown in F'ig. S, and com-
I)rises large nickel-plated binding posts 16
and 17 mounted about two inches apart, center
to center, on any suitable material so
as to support the electrodes 19 and 20. To
19 a brass rod one eighth of an inch in
thickness, is fitted a crystal of silicon 21,
cut in the form of a truncated cone. Its
base is glued to the rod, the electrical connection
being made by wrapping the joint
between the brass rod and the silicon with
tinfoil. The electrode 20 comprises three
inches of flexible cord, scraped of its insulation,
then bent double and tightly twisted,
the loose ends being cut off evcntly. I f
the end of the silicon can be ground smooth
without destroying its sensitivity a polished
brass rod may be used.
This makes a detector costing about 3.t
cents to construct. It will have a highly
finished appearance, exceptional reliability,
unusual sensitivity and require very little
adjustment, as the parts are fixed permanently
in place. Those trying this form of
detector resembling the early "E. I. Co."
Auto-coherer I am sure will be well satisfied.
After eleven years of experimenting
with all forms of commercial detectors 1
have found this one the only t>i)e constant
enough for quantitative measurements.
Flaving described one set of apparatus
adapted to be operated according to my new
method of tuning I will now briefly describe
the characteristics of crystal detectors and
tlie theory of operation of both thermoelectric
and ionic detectors, in order more
clearly to disclose the exact nature of my
new method.
.\ Tliermo Detector consists of a very
fine point or "cat-whisker" resting upon a
thermo crystal with a comparatively light
contact. When an alternating current
passes to and from the crystal, heat is generated
in minute quantities at this point.
This heat causes a "thermo-pile action" and
generates a thermo-electro-motive force.
Impulses of alternating current coming into
the detector in such direction that their
direction is the same as that of the thermo
e.m.f. are allowed to continue and pass on
thru the circuit. Those passing in the opposite
direction are opposed by the thermo
e.m.f. and are supprest or '^'iped out. The
impulses which reach our 'phones then are
always in the same direction as the thermo
e.m.f. Thus is accomplished the rectification
by thermo crystal detectors. These
crystals always require a metallic point and
to this class of thermo crystals belong the
following : copper pyrites, tellurium, manganese
dioxid, chalco-pyrites, galena, iron
pyrites, etc.
Ionic detectors are also rectifiers but perform
their function in a different manner,
these metal points not being necessary and
the form of contact being of relatively small
importance. These detectors have no useful
thermo e.m.f. A large polished plate of
the crystal may be placed between two highly
polished electrodes and it will work equal-
ly well, if not better, than with a point. I
have taken a piece of nudybdenite one-half
inch in length and tacked it to a board with
a tack at each end. It worked very well as
a detector and required no adjustment. It
was not especially sensitive but its operation
was perfectly constant. On the contrary
an ionic detector rectifies by the polarization
of its contained ions, an ion being a
combination of a number of positively
charged molecules, with one negatively
charged electron.
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