By 1842, Britain was using two-thirds of all the coal produced in the Western world. In London the result was a near-impenetrable gloom through much of the year. In one of the Sherlock Holmes stories the detective has to strike a match—in daytime—to read something written on a London wall. So hard was it to find one’s way that people not infrequently walked into walls or tumbled into unseen voids. In one famous incident, seven people in a row fell into the Thames, one after the other.
