On sunshine, the sea and split ends.
Pouting down at me from a poster on the wall was a glamorous model, crowned with a shining fountain of impossible hair. A selection of different hairbrushes located to my left were laid out like a toolkit, primed for the pursuit of perfection. My own wayward mane kept falling into my eyes, betraying my utter ambivalence towards the hair care trade. But the hair scientist that we had come to visit was determined to extract my opinion anyway. He was gesturing at three shiny tresses of hair, perfectly combed and displayed under a bright light. He was asking a question: “Which one of these do you think is in the best condition?”. I was clearly about to fail the first test of hair care, because all of the tresses looked exactly the same to me. And then, just before I admitted my ignorance, my brain made the link with the ocean.
The mighty Pacific Ocean was my companion when I made the switch from my PhD topic to oceanography, and was introduced to the mysteries of our planet’s oceans. At the Scripps Institution of Oceanography in California, where I was based, the Pacific was the backdrop to everything. Every Friday after work, the scientists would gather at a wooden hut on a cliff, watch the sunset over the ocean and drink beer. It was there that I first noticed the sparkly line on the water’s surface when the Sun was low, reaching out directly towards me. It’s poetically known as a ‘glitter path’, as sunlight sparkles off the ocean into your eyes. And on this very same cliff top, decades earlier, two physicists had worked out that the glitter path carried information.
You can often see a glitter path on rivers and lakes as well as the ocean, whenever the Sun is low in the sky. And they vary in width. Sometimes you see a wide line close to the Sun, which becomes narrower as it comes in towards the shore. And sometimes it bulges in the middle, or near the coast. The water isn’t a perfect mirror, because it isn’t completely flat. If it was, then you would just see an upsidedown image of the Sun reflected in its surface. But that’s rare. A glitter path is made up of thousands of individual sparkles, as different waves catch the Sun’s image. Those waves can be slightly off to the side, or in front of, or behind the perfect image, and you see the sparkles as different waves catch the light coming from the Sun and redirect it to you. So the rougher the water is, the wider and longer the glitter path, because there are lots of different places that a wave can be and still bounce sunlight towards you. A narrow glitter path tells you there’s calmer water. Even though you can’t see the individual waves – they’re relatively small and they could be miles away – the glitter pattern is providing a measure of surface roughness.
And so back to the hair. An individual strand of hair is covered with tiny scales. On healthy hair, the scales lie down flat, but on damaged hair, they stick out at all sorts of funny angles. One of the hair tresses was reflecting the bright light in a really narrow line, and the others were wider. The same principle was at work both here and on the ocean – I couldn’t see the scruffed-up scales on the damaged hair, but I could infer their existence from the shine pattern. I pointed at the one with the narrow shine pattern, and the hair scientist beamed at me. Maybe there’s hope for me yet in the world of hair care.