Andrew Sullivan on the origins of the word “log” in the “an official record of events” sense, from which we derive the word “blog”:
A ship’s log owes its name to a small wooden board, often weighted with lead, that was for centuries attached to a line and thrown over the stern. The weight of the log would keep it in the same place in the water, like a provisional anchor, while the ship moved away. By measuring the length of line used up in a set period of time, mariners could calculate the speed of their journey (the rope itself was marked by equidistant “knots” for easy measurement). As a ship’s voyage progressed, the course came to be marked down in a book that was called a log.