When Isaac Newton allowed the sunlight passing through a hole in his blind to hit a glass prism that split it into different colours, he wasn’t the first to see such colours. In fact, he’d probably seen them as a child, reflected from the bubbles in his bath, and of course in the colours of the rainbow, which appear when white light is split up by being bounced around inside raindrops.
Newton was the first, however, to think of using a second prism to put the colours back together again, and hence to prove that white light is made up of many different colours. But how many?
It depends on your imagination. To the mediaeval mind, there were just five colours in the rainbow: red, yellow, green, blue and violet. But Newton added two more – orange and indigo – because he believed that the harmony of colours in the rainbow must be similar to the harmony of notes in a major musical scale. Seven steps in the scale; seven colours in the rainbow. Newton looked for them, and he found them. It rather puts the lie to the old saying that artists see what they believe, but scientists believe what they see.
Image Attribution: Christine Matthews
I would add that in the medieval mind there were also seven planet and seven metals. The idea that the universe scaled and the very small was reflected in the very big is an important idea (see Dijksterhuis’s amazing book on the “Mechanisation of the World Picture”). The number seven is an important one in alchemy and even today the number seven seems to the top the list of “favourite numbers”.
That’s quite some assumption that Newton took a “bubble” bath as a child. I believe he may have been bathed occasionally. He may have even done so in a tub. I have a harder time believing that it was with a soap that created great bubbles. Lye soaps lack the modern surfactants that make all the bubbles somewhat stable, if I recall correctly. (But maybe I don’t.)
Newton discovered the “Newton black film” by watching the changing colours in soap bubbles, where the soap film gradually thinned until it became black. So the bubbles must have lasted a while, even if he wasn’t bathing in them. I have his original description somewhere, but it might take some digging out!