To me, the mirror screw is almost magical. But I am not the first one to say this. Upon seeing one for the first time, very few will have any idea of what the mirror screw was designed to do. Most if not all are surprised to learn that it actually will produce pictures, like the television set in their home. Very few have even heard of mirror screws before, much less ever seen one in operation. So if you have never seen a mirror screw in operation, you may, as many others have wondered... "WHERE DO YOU SEE THE PICTURE?" If the screw is not rotating, it is not obvious where one should look. Many have thought there has to be a screen of some sort, somewhere. If the mirror screw is rotating without the signal light on, one still can't be sure where to look. However, when the light does come on, no matter where you are, the picture will appear. This is because the mirror screw offers a field of view of some 150 degrees in the horizontal plane. Some have said, upon seeing it for the first time, that it seems like magic to them, the way it's able to put the picture together for all to see. In fact, I too find myself occassionly referring to them as "magic mirrors". I've built about twenty of them. I also
have put together numerous receivers using these mirror screws, so that I could demostrate to others, how well these television sets actually performed in the early 1930s.
Except for it rotating, there is actually no other motion involved. It's just a case of perfect timing. By keeping the speed of rotation exactly correct, the screw is able to place every picture element of a scene in its proper place, in yours and every one else's field of view. And that does sound a little like magic to me.
Here is a photo of an operating 32 line mirror screw receiver, set up as a demonstration at the Antique Wireless Association, a few years ago. The set is working here in normal room light levels ( as opposed to a darkened room) used for the display of equipment. The Felix the Cat figure is on a turntable while being illuminated by lights, mounted on a mechanical camera about 6 feet away. Notice that the shadow of Felix is falling on the surface behind him.
Shown below is a photo of the mechanical scanning disk camera, used to generate the picture now seen on the mirror screw receiver. This camera is equipped with a 12 inch diameter Nipkow disk. Signals from the camera are transferred to the receiver by way of a coaxial cable.