The original window glass, Roman glass, was mined from opal bearing ground. Hyalite or clear opal was extracted and shaped as a window allowing vision, but keeping out of the weather.


As mineral smelting improved artificial glass was made using silica, soda ash and some trace minerals. Lead was one doubtful addition, in spite of giving clear crystal glass.

Eventually glass was shaped to improve human eye sight, extending the vision of people into old age. Shaping glass into different shapes led to triangular prisms.

Isaac Newton found that a small hole in a window curtain, through a glass prism duplicated rainbows. He saw that white light was a combination of seven distinct colours.
This eventually led to the understanding of the huge variation of electro-magnetic waves, ie ripples on water.
An experiment of light shining through two slits onto a screen produced the anomaly of tree separate lines on a screen. This was proof of photons being both a particle and a wave.

Sunlight travelling through the atmosphere slows slightly and tends to the blue end of the spectum. The speed of air and speed of light are vastly different, better than the square of the speed of air as a number.