I have learned to be suspicious of measurements given in unfamiliar terms. (In a Simpsons episode, Grandpa boasts of his car’s fuel economy as so many “rods per hogshead.”)  Sometimes even using familiar terms, such as feet and seconds, can be confusing.  Your article on bats (“To Build a Better Batmobile,” Elms, March/April) breathlessly refers to their speed as “up to forty-nine feet per second.” Sounds fast, but that’s only about thirty-three miles per hour.  Lots of birds can fly faster than that. And we have little trouble observing vehicles traveling three times as fast, or jets traveling twenty times as fast. I imagine it’s their size, their rapid dartiness, and, of course, the dark that make them so difficult to observe, rather than their native speed.

C. Paul Minifie ’68

West Simsbury, Conn.