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US4149896A Phototropic glass for multifocal spectacle-glasses 失效
用于多焦点眼镜的光转向玻璃

Phototropic glass for multifocal spectacle-glasses
Abstract:
Glasses are provided which may be made phototropic and which have a thermal coefficient of linear expansion between about 43 and 58.times.10.sup.-7 /.degree. C. and an index of refraction n.sub.d over about 1.60. Such glasses can be employed as near portion glass material in spectacle lens manufacture; thus, such glasses can be fused with known phototropic for portion glass material, for example, of the borosilicate type, to make multifocal glasses useful in spectacle lenses and spectacles.
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