Reflections 9/25/96
Robert Kern Curtis

Piggy's Glasses

It is Golding's The Lord of the Flies about which we are thinking. While I do not agree with the basic Hobbsian premise of this story, I did enjoy reading it years ago and am happy that it is still read and discussed in high school English classes.

But the physics problem in the novel provides a glaring example of poor thinking. I refer to the fact that piggy's glasses are used to provide Prometheus's gift to the island on which the choir boys are stranded. A lens can be used to make a fire if it is a converging lens; a Fresnel lens which converges light (and heat) by diffraction can be extremely effective, so too can be a refracting lens, which is thicker at the center than on the edges. Such lenses focus the sun's rays at a point which Kepler called the focus--from the Latin word for fireplace!

Glasses which can so focus light (and heat) are commonly called reading glasses and are used by people who cannot see clearly objects which are up close--people who are said to be farsighted. In the story, however, Piggy's glasses are crushed and destroyed by some naughty boys. After this event, we are told that Piggy has trouble seeing things at a distance! That he is myopic, or nearsighted. The image the eye sees is focused on a point in front of the retina. To correct this condition, diverging lenses are used. These are refracting lenses which are thinner in the center than at the edges and these lenses do not form real images, and do not focus light or heat. They cannot be used to start a fire.

Thus we have a fundamental physics flaw in the story. I suppose that we have to give William Golding an F for this.


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