Newton was born on Christmas Day, 1642 -the same yaer that Galileo died. Something of a loner (perhaps due to a fairly unpleasant disposition), Newton did much of his seminal work in optics during a period reclusion in the English countryside while avoiding an of his findings in Opticks. Amongst the important findings detailed in this text are the following.
1. White light is made up of the complete spectrum of colours.
2.The colours can be separated out by passing the light through a prism, as different colours are bent (refracted) at slightly different angles.
3.This 'dispersion' (not his word for it) is the cause of the chromatic aberration that Huyguns found to be affecting refractor (lens-based) telescopes.
4.There is no dispersion when light is reflected.
5.Telescopes could be improved by using a reflecting focusing element (a mirror) instead of a refracting one (a lens), since all colours will focus at the same point. This type of telescope is now known as a Newtonian reflector.
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Chapter 2 - Page 33