the life of Philo T Farnsworth - Early Television Foundation

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THE STORY OF TELEVISION
cians were employed and set to work by Phil in the design of the
transmission and receiver apparatus. were not trained
They
engineers. They, like Gardner, learned of the problems in television
as they went along.
The transmitter tube, which was to break down the picture
and convert it into an electron image for transmission, was
Farnsworth's first concern. As I have already mentioned, he
conceived it as a cylinder about the size of an ordinary Mason
jar with an optically clear window sealed into one end and a
photosensitive plate at the other end. As they got into construction
on this tube, two major
difficulties were encountered.
One was the art of sealing in an optically clear flat disk of glass
at one end of the tube without leaving stresses and strains in
the glass that would cause cracks under hard vacuum when the
tube cooled and was subjected to varying temperatures. The
other was the distillation of the photosensitive substance on
the plate at the rear of the tube. Incidental to these two major
problems was the difficulty in getting the right type of electrical
leads in and out of the tube so that it
would operate as the
inventor had planned.
Phil decided that the tube was to be known as the Farnsworth
"dissector" tube. This name was chosen because it was de-
down the
scriptive of the process that took place in breaking
image for transmission.
Potassium hydride was used as the photoelectric surface in
the early dissector tubes. Since potassium combines with oxygen
when exposed to air or water, the potassium pellets
came
from the suppliers submerged
in kerosene. Gardner had to
learn the art of distilling the pure potassium from the commercial
pellets
and sealing it in airtight glass tubes for future
use. To deposit the potassium on the rear plate
of the tube as
the foundation for the photoelectric surface, in building the