Who was the first person to introduce a system of making books with raised letters for the blind?
If you're not asking how companies that make keyboards produce raised letters on the keys, then please be more specific. There are a couple of ways this could be done. The letters could be molded in. I'm not aware that anyone actually does this, but it would work. The ink used to paint the letters on has a certain thickness after it dries. By carefully choosing the ink used, this can produce noticeably raised letters.
They use braille Braille is an arrangement of raised dots on a surface that form numbers, letters, and words. Blind persons feel the dots with their fingertips to recognize the patterns. The technique is similar to holding a pair of dice in your hand and feeling the dents that tell you what number is on each face. You can feel how many dents there are, which tells you what number it is. Braille is the…
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When a thick glass slab is placed over some printed matter the letters appear raised when viewed through the glass slab. Why?
When we keep the glass slab over some printed matter, the light coming from the letters (after reflection ) face change of medium at glass-air interface. Since glass has more refractive index than air, the light bends away from the normal as it goes out of glass. This apparently causes us to see the letters raised. Hope this clarified your doubt.