Theory of Colours, by Johann Wolfgang von Goethe (TPB, 2000 edition of 1840 book, $3.25)
And here I was thinking Goethe was just the writer of Faust. Once again I am humbled by my ignorance. Goethe was not just a writer, but also an artist, biologist, theoretical physicist and polymath. He studied and wrote papers on plants. He collected minerals, and had the largest private collection in the world, almost 18,000 rocks! He started out as a painter, became a lawyer, was fired, went on to biology and writing, returning eventually to the study of color. He said he was never proud of his writing, only his discoveries on color, which made him superior to anyone else. Ironically, his work on color turned out not to be scientifically important, but Darwin studied his works on plants, and we all still know and study Faust. I wonder what he would think of how things turned out.
Look for this book on the new non-fiction table.