A fish and a theatre light

I was reminded of a favourite story the other day, when preparing to give a speech to the NZ Association of Scientists at the their annual conference. The point I hope to make was the power of story telling in education, and in particular how the stories of science can be a fabulous hook when it comes to interesting young students  in science. As it happened, I never got to the the story during the presentation, but the  urge to recount it remains:

At the beginning of the 19th century, the popular theory regarding the behaviour of light was that it behaved as a particle. this popularity was due, in no small part, to the fact that Newton had said did, and what Newton said tended to go. Geniuses are never wrong, right?  As is the way in science, there remained a number of unresolved problem with this light theory, and one of them was how to explain the way light bends as it passes through media of different density (think of the way a straight tick put into a stream appears to bend). The French Academy held a competition to explain this. An entry came in from Fresnel, and engineer, who explained it terms of light traveling not as a particle, but as a wave.

For we theatre folk, Fresnel’s name is entwined with the business of lighting the stage, as he invented a lens that is utilised in theatre lighting (and light houses I believe) and still carries his name. The esteemed members of the judging panel were initially sceptical of this unorthodox, outsider’s view, and in particular the renowned mathematician Poisson (he has a probability distribution named after him) is said to have mocked Fresnel’s entry. in order to demonstrate how preposterous it was, he noted how one can not shelter behind a rock to protect oneself from a wave in the ocean, because waves, by their nature, can wrap around the rock and collide behind it.

Going further, he used Fresnel’s own calculations to show that if he was right, it predicted that if you shone a light source directly at a solid object, then at the right scale you would observe the brightest spot of light directly behind the solid light, in the area shielded from the light source. Preposterous.

Luckily for science, another member of the panel, Aragol, thought it judicious to set up exactly this experiment. no surprises for guessing what happened next. The spot appeared, exactly where predicted, and the wave theory of light was resurrected. For the science geek, this story has everything. The historical authority figure, the powerful cheerleader, the preposterous prediction and yet crucially, the experimental observation which triumphs these most potent forces of intertia. In science, or so we hope, data trumps prejudice.

Of course, history shows progress is rarely this clean, but nevertheless messier versions of the principle are the happy norm. Meantime, this case stands for me was, well, a beacon



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