Why do we measure boat speed in knots?

As you know, sailors have been doing their thing for thousands of years (the first known rendering of a boat is from 5500 BC ). From the primitive animal skin that may have been used to propel a man on a log across a lake to modern day yachts that can approach 40 knots on the open sea, we have some very archaic sailing terms that have been with us for a long time. How did they originate? Simple terms like cockpit (origin obvious), shroud and cunningham. Let's take a look at a term we all use when we go sailing. "How fast is the boat moving?" "14 knots, Captain", comes the reply.  Knots refers to nautical miles (knot is one nautical mile per hour (1 knot = 1.15 miles per hour)) . It corresponds approximately to one minute of latitude along any meridian. Knots per hour was originally derived from a practice used in the 17th century.  To guage the speed of the ship, the crew would use a coiled length of line with uniformly spaced knots every 47' 3" (or 8 fathoms). The chip log (a piece of pie shaped wood) would be thrown into the water and the rope was allowed to payout freely as it trailed off behind the ship. The number of knots that passed off the stern of the ship and into the water in a given time (sand glass for 30 seconds) would determine the speed of the ship. Is that cool or what? It's fun to tell your sailing friends this story when out on the water as most donot know this piece of history. They will be amazed at the depth of your sailing knowledge!