the life of Philo T Farnsworth - Early Television Foundation

26 THE STORY OF TELEVISION
Tolman could see what he was driving at, as eagerly he strove
for approval.
Tolman understood and told the boy that it
sounded reasonable.
Then came the problem of receiving the image in the home.
Farnsworth's idea was to build a receiving set around the
cathode-ray tube. To do this it would be necessary to devise
means by which the picture signal radiating through the ether
could be detected by the household television set in a manner
similar to that used in sound radio.
Amplifiers would be required
to build up the electrical current representing the picture
values and feed it into the cathode-ray tube.
The tube which Phil proposed to use as the heart of the
receiving set was a pear-shaped vacuum bulb with a slender
stem. A current flowing through and heating a filament in the
stem gave off the electrons which formed the invisible cathode
beam. Phil visualized this beam as proceeding in a straight line
to bombard the fluorescent surface lining the opposing bulb
end of the tube, thus causing
it
to glow. This completed the
cycle of translating electrical current back into light values,
which in turn would reproduce the original image for viewing
in the home.
To provide the lights
and shades of his picture,
Phil reasoned
that if he put a shutter in the stem of the cathode-ray tube to
control the flow of the beam it
would be possible to use the
varying picture current coming from the transmitter to operate
the shutter, or grid. However, it would be necessary to focus the
beam and oscillate it for scanning. Here again Farnsworth's
inventive mind provided a magnetic lens in the form of a coil
around the stem of the tube to bring the beam to
pinpoint
sharpness. Magnetic scanning coils similar to those at the transmitter
would also be provided. Operating in exact synchronism
with the pulses at the transmitter, these coils would control