— Fulsome prism blues

THE ACT OF BUYING a small prism – easily available from educational suppliers and science-themed gift shops – is a gesture that resonates with historical significance.

After all it was Isaac Newton himself who in 1666 manipulated one, such that white light entered one side and a multicoloured stream flowed from the other. It was a potent demonstration that led to the understanding that changing the wavelength of light – by bending its path as it passes through an object – causes different degrees of refraction and thus the revelation of the rainbow.

Living as he did in a world without electricity and thus in an environment free from multiple sources of artificial illumination, it would be quite reasonable to expect that Newton achieved his prism trick rather more easily than most of us can in the world today.

Upon buying a prism – small, made of glass or plastic, with a triangular base and rectangular sides – and getting it home, it is perfectly natural to try to generate a spectrum. Some people, of course, do this in homage to Newton, while others, perhaps, are more intent on reproducing the image from the cover of Pink Floyd’s album Dark Side of the Moon.

Either way, for many it quickly becomes apparent that in the modern world the task is easier said than done. The room needs to be completely dark – a remarkably difficult state to achieve in a 21st century house. Quite often, heavy drapes and gaffer tape need to be procured and deployed.

The beam of light also needs to be very narrow. Most torches, it is quickly discovered, send out beams wider than the prism, masking the effect.

Shopping trips in search of tiny torches frequently result, prompting the question: where do you buy a torch with a beam so narrow that its only conceivable purpose is to bounce through a prism in a dark room?

Thus often, by the time the necessary preconditions for one of the foundation demonstrations of classical physics have been met, exhaustion and frustration may be more prominent than enthusiasm.

In the end, though, it is all worth it. The spectrum stabbing out from a gorgeous little piece of geometric glass is a beautiful and breathtaking sight, even in miniature. It looks like an act of magic – except, of course, we know that it isn’t. It is an act of science.

And that’s the whole point.