There's been a lot of research on what happens to a river when dams go up, but what happens when the dam comes down? With support from the National Science Foundation, Dartmouth College geographer Frank Magilligan is researching the impact of dam removal. His lab has been the relatively small Homestead Dam, built more than 200 years ago along the Ashuelot River in New Hampshire. He and his team have collected data on the ecology and geology of the Ashuelot River both before and after the Dam...

TIME DILATION: an experiment with mu-mesons This classic film documents an experiment done in 1963 the results of which can only be explained when one accepts the consequence that moving clocks run slow. This phenomenon is known as time dilation. The timekeeping device is the mu-meson, a subatomic particle with origins away from the Earth moving at relativistic speed. What follows here is an explanation of the experiment described in that film. Many mu-mesons rain down every hour on the...