Ground-water levels in pennsylvania make notable recovery from extreme low stages
- Book ID
- 104132340
- Publisher
- Elsevier Science
- Year
- 1940
- Tongue
- English
- Weight
- 108 KB
- Volume
- 230
- Category
- Article
- ISSN
- 0016-0032
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✦ Synopsis
Polaroid Variable Day Glass arises from three facts: (I) Many scenes in ordinary life are too bright for comfortable and efficient vision. (2) The degree of brilliance of different neighboring scenes may vary in large measure. (3) There is a great variation from person to person in tolerance of excessive brightness over extended periods. Unlike any previous device, it makes any brightness right for any normal eyes. With it each eye looks out through two Polaroid lenses. The front lens before each eye is stationary in the frame, while the two rear lenses may be rotated by a convenient button on the bridge of the frame. When this control button is moved to the extreme left, the maximum amount of useful-seeing light reaches the eyes. As the button is moved towards the right, the glasses become gradually darker and darker, until at the extreme right they are so dark that the brightest possible surrounding landscape can be viewed with no discomfort whatsoever. Between these two extremes of adjustment lies an infinite variety of densities --at least one of the densities is sure to suit the eyes. In effect, the Polaroid Variable Day Glass is the equivalent of a whole series of conventional glasses, carefully graduated to pass different amounts of light. In addition to their revolutionary control over brightness they have the optional feature of louvered side shields. The louvers, like Venetian blinds in the plastic shields, effectively block out light that causes back reflections, and transmit light that makes possible clear side vision. Side shields on eye glasses are not a new device. However, these new louvered side shields are the first ever devised that both completely block back reflections, and permit the clear side vision that is so important for automobile driving, boat racing, and other outdoor pursuits.
R. H. 0.