With the dramatic differences between daytime and overnight temperatures these days, I've been able to enjoy a curious phenomenon on my way to work. On the border of Bedford I cross over the Concord river, the waters of which have lately been first chilled by the frigid autumn evenings and then warmed by the quickly-heating early-morning sun. This abrupt shift in temperature produces a very local fog, which rises to a hight of perhaps 100 feet and reduces visibility within its bounds to under a quarter mile. Under a quarter mile left and right, that is; the whole band of cloud is only a little bit wider than the river, and the Concord is not, at that or any other point, a mighty Mississippi. So about two seconds at 40 miles an hour. It's very pretty; the overall effect is something you might see in a fantasy movie. It's like crossing into the faerie land of Carlisle, MA!