Isaac Asimov routinely penned science essays in various magazines, and given his eagerness to publish books, often produced collections of said science essays. The Planet that Wasn't is one such collection, covering pure science as well as science's perception in society. The title essay refers to the speculated planet of Vulcan, which was thought to exist between Mercury and the Sun, proposed as a way to account for Mercury's slight orbital deviation. Vulcan could never be found, because it did not exist: our entire understanding of physics had to change (from Newtonian mechanics to Einstein's relativity) before Mercury's orbit was truly understood. After some initial astrophysics, a brief series of essays takes us from the versatility of carbon to biochemistry, and Asimov devotes a chapter to the working of the gallbladder, cholesterol, and high blood pressure. The latter essays move from science to its relationship with society: "The Nightfall Effect" addresses the notion that human beings can only settle outer space on other planetary bodies, and not space stations, while "The Flying Dutchman" tackles UFOs. My favorite essay is "The Bridge of the Gods', which addresses the physics of the rainbow and treated me to a history of optics.
Enjoyable as ever, but I would say that...being an Asimovophile.