Colour and the Prism

We are taught at school that a prism splits White light into its component colours. This is not true. Pass White light through a prism and you get White light. You cannot see a spectrum through a prism unless there is an edge visible. It is the edge that creates the colours, by reducing the energy of the light passing the edge, in the same way that water passing through an orifice has a reduced flow-rate adjacent to the edge of the orifice.

“Grimaldi has inform’d us, that if a beam of the Sun’s light is be let into a dark room through a very small hole, the…, and that these shadows have three parallel Fringes, Bands or Ranks of colour’d Light adjacent to them.”

From Sir Isaac Newton’s ‘The Third Book of Opticks’, fourth edition, first paragraph, originally published 1730, Dover Publications, Inc, New York. Standard Book Number: 486-60205-2

It is clear therefore that the creation of colours by an edge has been known to science for nearly 300 years. However I have never seen any mention of this in any modern book on physics.

This discovery by Grimaldi – Italian physicist – (1618-1663) was  quite important, but its main significance was missed by the physics establishment, (Possibly not true of Newton, because he was quite devious in many ways, and his inclusion of the above paragraph as the introduction to Book Three would indicate that it had particular importance to him.)
It is also obvious from the above that the edge creates THREE colour bands, not 6 or 10 or 20 or 50. These bands are the Dark Blue, Red and Yellow referred to in this web site. from which all other colours are derived.  Although you can understand it being missed 300 years ago, there is no excuse in modern times for this evidence being ignored. The problem was (and still is), that it had already been accepted by the physics establishment that White light was a combination  of all the  other colours.

These coloured edges are commonly visible when looking through windows at a bright sky. The window is a wide slit. The shadows on both sides of a beam of light coming through a slit have coloured edges. We should really say that the White light passing through the slit has differently coloured edges.

A prism does not split White light into the different colours. but makes  the colours created by the edges of a slit more readily discernible. If the slit becomes too narrow the coloured edges meet and give the distorted and blurred spectrum that physicists claim as a ‘true spectrum’.