We aren’t entirely sure why Newton came up with the number seven, including those obscure shades indigo and violet, but there’s a strong feeling that he was drawing a parallel with music. In the musical ‘spectrum’ there are seven notes, A to G, before completing the octave and returning to the next A up. Newton, it’s thought, felt that there also ought to be seven colours in the visible spectrum.[loc. 1323]
Entertaining pop-science, just the right length for a 4-hour flight: Clegg explores cloud formation, fractal coastlines, the physics of flight, airport security technologies, volcanoes, oxbow lakes ... It's a light read, with plenty of anecdotes and examples: possibly I was not the target audience, but it passed the time and some of the information was new to me.