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and reaches the first black line No
light is reflected from black and none
reaches the photoelectric cell The
cell gives forth no current: none
reaches the neon tube. and the light
goes out. The hole on the receiving
scanning disc has moved a correspond
ing distance to the left, and at that
point the eye sees shadow. Thus as
The hole moves across the top edge of
the aperture the eye sees first a streak
Of light. then darkness. then another
streak of light. and so on until the hole
has completed its course across the
aperture.
The next hole starts across on a line
bit below the first one, and reveals
light and shadow in the same manner
There are so of these holes in all, and
when the disc has made a complete
revolution the entire picture has been
revealed. Since the whole process
takes but one-twentieth of a second,
The eye. because of persistence Of
vision sees all so streaks of light and
shade apparently at once. Conse-
quently it receives the illusion of
number of vertical black lines-the
same as the picture being transmitted
When the subject moves the televisor
gives a rapid succession of these images
just like a motion picture protector.
In its present state of development
television does not give perfect image
Minute imperfections in the scanning
discs, together with their rapid rota-
tion, give a somewhat blurred effect
1t Is about as clear as the average
newspaper halftone would be If it were
animated.
NNE of tbe Croo taSt ,orOhIa,,os -, to1o
vision was that of synchronization
The two scanning discs of the system
must run at precisely the same speed
and keep in step. Each scanning disc
is operated by main motor. At the
receiving station synchronizing
generator is mounted on the same
shaft with this motor; at the sending
end the Synchronizer Is another motor.
designed to keep in step with the
generator from which it receives its
power.
Thus synchronism is assured. The
motor at the receiving end operates a
generator. This generator transmits
its current to motor at the sending
end which Is mounted on the same
shaft with the main motor. II the
latter drives the discs too slowly, the
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up, keeping in step with the generator
at the other end, or conversely retards
its action when it goes too fast. Since
| the generator is driven by the receiving
station motor, the speeds of all four
machines are Identical
To transmit motion pictures similar
apparatus is used. Motion picture film
is employed as in the usual protector.
but the beam of light passes through
a scanning disc before reaching the film.
Behind the film is photoelectric cell
Thus a thin pencil of light traverses
each film, and the resultant light and
shade find reaction in the cell. The
film is scanned at the rate of 16 pictures
a second.
| At the receiving end a mercury-arc
| lamp, which gives a much more power
| full light than the neon tube, projects
the image through scanning disc on
| to a screen. The use of the arc light
was made possible by an arrangement
| similar to that in radio tube. where
! the weak grid currents control the in
| tensity of the more powerful battery
current. The arc lamp dims or bright
ems instantly according to any variation
in the faint currents coming from the