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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