Show s t carll Clr ll aldma mohave been the first to recommend the nse of blua glass bat they were at first more widely in dennany Gen nany chiefly recommendation the great oculist grate 0 bohm ana others blua color ct glasa is chiefly to be mended because it absorbs those rays la choir passage which belong to the belloir and orange portion of the spectrum in which the greatest brightness aad greatest heat are concentrated arid thee yea especially weak ones consequently greatly protected by the blue while rays which such eyes are able to bear obtain access the material for bine glasses which hao to be made in various shades to suit individual eyes is somewhat lasa hard than that employed formerly for green spectacles ind is also inferior in that respect to white glass but it has gained in durability compassed with former descriptions of glass still greater is the progress recorded in the manufacture and hardness of smoked glass also used for protecting the eyesight this kind of glass discolored Is colored gray or mouse colored by the of manganese formerly suffered acom oo greak by the addition 1 acta larse quantity of lead but the bet manufactures now made are newly equal to abita glasa in point of hardness the object of smoked glass is f reduce the glare of light without gating colors chambers |