Radio Craft Magazine, April 1936
The cover of Radio Craft magazine from April, 1936 depicts a
scientist viewing a new type of "electron image tube."
This was not a television tube in the modern sense.
Some essentials are there, however.
The left end of the tube has a photoelectric cathode layer
that emits electrons in a pattern mimicking whatever that
end of the tube "sees." The electrons pass through the
tube and light up a flourescent layer at the other end, making
a visible image.
In this cover painting, the image tube is "looking" at
the eyepiece of a microscope. The scientist views the same
image (perhaps minus some level of detail) that he would
see by looking directly into the eyepiece.
You could perform the same trick with a telescope, to
display the telescope's view on the image tube's screen.
What's exciting about that? And why wouldn't the scientist just
scoot his chair forward to look directly into the microscope?
Well, for one thing, the tube can be made responsive to
light wavelengths—infrared and ultraviolet—beyond the range of human vision.
For microscopy, these wavelengths might allow a scientist to view
details in living
specimens that would otherwise be visible only by killing the specimen
and staining it with dyes.
For telescopy, infrared would allow "night vision"
that senses heat rather than visible light. Infrared can also penetrate fog,
smoke, or clouds, making it useful to military, as well as scientific,
applications.
Hence, this little tube paved the way for a host of imaging
devices that we take for granted 70-odd years later. These
include night vision goggles, satellite imaging of Earth using
non-visible wavelengths,
and many other astronomical devices.
The tube was demonstrated to the American Association for the
Advancement of Science by Dr. Zworykin, a pioneer in the development
of modern television. His demonstration showed infrared and ultraviolet
imaging, as well as moving images taken from film.
What's missing from this picture? Distance. The "tele" part of
television means distance. This tube could only portray something
that it viewed directly.
To send that image far away,
Zworykin and others had to add some means for deconstructing
the picture into electronic waveforms, broadcasting them through the
air, and reconstructing them into a picture.
This was eventually accomplished by using a TV camera at one
end to receive the image. That corresponds to the left half
of this tube. Complex circuitry then encoded the picture
as waveforms, and a transmitter sent the signals through the air. At
the receiving end, the television used complimentary circuits
to decode the signals and show them as an image. The final display
corresponds to the right half of this tube.
This is not a TV, in short. However, this experimental
tube marks a major milepost in developing
a broad array of electronic imaging devices, of which
television is one.
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