The Demonstration Eye dates to the 19th century and was the first device to let the doctor experience eye problems from a patients point of view. The eye is first adjusted for normal vision by pulling out the brass draw tube. This has a ground glass screen on one end on which the image of an object is formed. To simulate near-sightedness, the tube is pulled out, and the negative corrective lens is swung into place to compensate. Far-sightedness is simulated by pushing the tube in and using the positive corrective lens. The large picture above is the Radio-Guy Museum‘s newest addition. The 5 smaller pictures are other known examples. Left to right: CuriousScience.com, Transylvania University, Smithsonian Institution, Bates College and Thomas B. Greenslade, Jr. collection.