Evening star., 1928-10-28
BY WILLIAM NJ. LAAS.

A LMOST every day now one reads
~ about a demonstration of tele-
"A vision, the newest marvel OF
4 4 fast-stepping science. The radio
fan prophes1es glibly that 1t
won't be long before his set viii be re-
ceiving pictures as we'll as words. But
how many know what it's all about.
What do all these new developments
mean, and how does the thing work
anyway? If 1t does work, why cannot
one buy little televisor and use 1t in
his own home?
Studio scenes are now regularly
broadcast by television from certain
large radio stations, and eager anna
teurs are already building their own
sets with more or less success from
directions in the radio magazines. But
television is still in its infancy. just as
auditory radio was around 1914. It is
hardly out of the laboratory, too COM
plicated in operation for all but the
skilled experimenter, and too expensive
for the average home. Years must
elapse before television becomes an
everyday factor. although constant ex-
Fermentation is gradually eliminating
the obstacles in the way of its develop
ment But it is coming, and coming
sure. So be prepared
To understand the process of tele-
vision one must look into the workings
OF its EYE" the photoelectric cell. This
mervelouS device. invented only a few
years ago, today performs innumerable
different little jobs for commerce and
science. BY its power of reacting cleo
trically to light it measures daylight or
the progress of stars, it counts traffic
on the streets and selects cigars accord
Ing to color. In talking moving pic
lures 1t changes light to sound. and in
television transmutes light variations
into electric impulses.
To explain this one must go back to
the first principles of the molecular
and atomic theory. 1t appears that all
matter is composed of atoms, which. in
turn, are made up of electrons and
protons, normally in equal numbers.
Under this condition of equilibrium an
atom Is ncharged-electrically neutral.
When an atom loses one of It's
electrons it tends to attract toward
itself any neighboring electrons and
thus is positively" charged. If. on the
other hand, the atom has an extra
electron, this electron tends to draw
away from it and the atom is mega
lively" charged. Connect by a wire a
body composed of positive atoms to one
made up of negative atoms and the
electrons will stream from negative to
positive until equilibrium has been re-
stored. This current of electrons is
what constitutes electricity.
X X x X
NOV certain metals such as potas-
sium and caesium, have the prop
erty of emitting electrons when acted
upon by light. Expose a bit of potas-
sium to light and electronS will leave
its surface in large numbers. If these
electrons could be trapped in some way
into an electric circuit their movement
would cause an electric current Since
the number of electrons leaving the
potassium is proportional to the inten-
sity of the light, the current in turn
would be large or small as the light
dimmed or frightened
The photoelectric cell is glass tube
inclosing an almost perfect vacuum.
Part of its inner wall is coated with a
ight-sensitive metal, say potassium.
Suspended in the center of the tube
and carefully insulated from the potas-
sium coating is ring of some ordinary
metal, usually platinum. The metal
ring is connected to the positive ter
minal of a battery and the potassium
coating to Its negative terminal.