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