This summer my family and I travelled to Rome. While the temperatures didn’t reach the usual astronomic heights, it was rather warm. But we, and other visitors, didn’t have to worry about thirst. Rome has the best network of public drinking fountains that I have ever seen. Every few blocks, there’s a beautifully-designed basin with a spigot of continuously running water (I know, being from California, the never-ending stream made us very uncomfortable, too). There are two bits of information that have to be passed on to the first-time visitors of Rome: the water is potable—safe to drink, and how to use the fountain—there’s a bit of a trick to them. Above is my son demonstrating a little secret interaction. There’s a small hole on the top of the pipe that can serve as drinking fountain if the main hole at the end is plugged up (with a finger). While we learned about the great drinking water in Rome from many traveling guides (books, online sites, etc.), we obviously didn’t know about the trick until we watched a pro do it. Knowledge Propagation Circle Information propagates through communities. When we first encounter a novel bit of data, it tends to…