Throughout history, Britain’s scientists have often been motivated by one thing. Indeed some argue it’s perhaps the greatest driver of scientific discovery – the simple aspiration to understand how nature works. In its purest form it is just that, the desire to understand without any regard at all for how useful the discoveries may be, or how profitable. This approach to science is called curiosity-driven research, sometimes blue-skies research.
And the best example of a practitioner of this pure form of discovery is probably John Tyndall, who had a passion, it should be said, for the great outdoors.
Professor John Tyndall
John Tyndall was born in 1820 into a working-class family, but he ended up at the heart of the scientific establishment. He was appointed a fellow of the Royal society aged 32 and became Professor of natural philosophy at the Royal Institution a year later.
But as well as being a scholar, John Tyndall was also something of a romantic. One of his favourite places to find inspiration was the Alps. Indeed, the spectacular alpine landscape prompted one of his greatest discoveries, which in turn inspired generations of scientists to pursue fundamental research.
Tyndall wrote about the beauty of the mountains in this wonderful little book, ‘Hours of Exercise in the Alps’. He writes, “They seemed pyramids of solid fire. As the evening advanced, the eastern heavens low down assumed a deep purple hue above which, and blending with it by infinitesimal gradations, was a belt of red, and over this again zones of orange and violet.”
But John Tyndall was also a scientist, so he understood that whilst there is an aesthetic beauty to nature, there is a deeper beauty. A beauty that lies below the surface, a beauty in understanding how and why things happen. So Tyndall set out to understand the origin of those magnificent colours.
To do that, John Tyndall designed an experiment that he hoped would provide the answers.
Obviously a tank, and into that water I’m just going to put a few drops of milk. Note that basically just introduces some particles into the liquid. Now what Tyndall then did was shine a white light into the tank, and you immediately see that the tank lights up with different colours. John Tyndall loved this. In his typically poetic fashion, he described it as “sky in a box”. You see that at this side of the tank, then the solution is a blue and as you move through the tank, then it becomes more and more yellow and, actually to us, this end, it’s even beginning to become orange. So this is the alpine sky in a box, and Tyndall had an explanation for why this happens.
So there’s the tank and here’s a source of white light, which as Tyndall knew, is made up of all the colours of the rainbow. Now what Tyndall proposed is that the blue light has a higher probability of bouncing around a scattering of the particles of milk in the water. We now know that this is because blue light has a shorter wavelength than the other colours of visible light, making it more likely to scatter. So that means that the blue light will be the first to scatter and get dispersed throughout the liquid, and so the first piece of the tank will look blue. This is essentially what happens in the sky.
Instead of droplets of milk, Tyndall believed that blue light from the sun was more likely to scatter off particles of dust and water floating in the atmosphere, and so colour the sky blue.
But the tank also explains the sunset colours. As the light penetrates deeper into the milky water, eventually all the shorter wavelengths of blue light are scattered away, leaving just the longer wavelengths of orange and red, so the water looks progressively more orange and, if the tank were long enough, red. So, too, the sky. As the sun gets lower, its light has to travel through more atmosphere, so the shorter blue wavelengths scatter away completely, leaving just the orange and red light, making the sky appear red at sunset.
Now Tyndall’s explanation was right in principle but wrong in detail. See, Tyndall thought that the light was scattering off particles of dust in the air. In fact, it isn’t. It’s scattering off the air molecules themselves, but Tyndall couldn’t have known that because the existence of molecules wasn’t known at the time.
But it didn’t matter and, in fact, it was the misinterpretation of his results that led Tyndall to make his most important discovery of all, and it had nothing to do with the colour of the sky.
Being a curious scientist, Tyndall decided to proceed and carry out more experiments, so he took a box of air filled with dust… And he let the dust settle for days and days and days. He called his sample with all the dust settled out “optically pure air”. And then he started putting things in the box to see what happened. So he put some meat in it and he put some fish in it, and he even put samples of his own urine in it, and what he noticed was something very interesting – the meat didn’t decay, the fish didn’t decay, and his urine didn’t cloud. He said that it remained as clear as “fresh sherry”.
Now by allowing the dust to settle out, Tyndall had also inadvertently allowed bacteria to settle out. He hadn’t just created dust-free, or optically pure air. Without realising it, Tyndall had sterilised it. He’d let all of the bacteria settle out and stick to the bottom of the box. The air inside was now germ-free.
It may not have been his original intention, but Tyndall had provided decisive evidence for a controversial theory of the time, and that is that decay and disease are caused by microbes in the air.
John Tyndall was a man who followed his curiosity for its own sake, not for where it might lead. He didn’t set out to discover the origins of airborne disease when he began exploring the colours of the sky, but that is exactly what he did. It’s appropriate then that curiosity-driven investigation like this is often called blue-skies research.