Isaac Newton

Around the year 1666 a scientist called Isaac Newton wanted to do some investigations to find out about sunlight and colours.  

Isaac Newton

Isaac Newton 1642-1727

Courtesy of www.universityscience.ie

Isaac Newton
Courtesy of www.universityscience.ie

Isaac Newton

Isaac Newton 1642-1727

Courtesy of www.universityscience.ie

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Newton was not the first person to notice this; other people had seen it too, but they thought that the colours came from the glass, not from the sunlight. Newton decided to do some more tests.

He got another prism and allowed each of the colours (from the first prism) to shine through it, one at a time. He found that the second prism could never change the individual colours. He concluded that the colours were all present in white light. In order to test his theory he projected the spectra from several prisms onto the same area of the screen so that the colours crossed over each other (overlapped). A white patch was produced in the centre. This made him believe that white light is made up of the colours of the spectrum.

Colours of the rainbow

When white light shines into the prism the different colours are bent different amounts; as a result they get separated from one another and we can see a spectrum. Violet and blue are bent more than yellow and red. Newton named the colours he saw red, orange, yellow, green, blue, indigo and violet. These are also known as the colours of the rainbow.

There are of course many more colours in the spectrum. Most people can distinguish thousands of colours and naming them is a problem. There are also many other colours that are not in the spectrum, such as the many shades of brown and pink.

You don’t need a glass prism in order to observe the spectrum. It is much easier to see by observing the light ‘reflected’ by a CD, especially if the light source is long and narrow.

Why not try to do this experiment, as if you were Newton ?