Newton Gravity Glass

Our three-minute timer is an elegant desktop curiosity, sure to invite many questions. The hand blown amber hourglass contains white sand and floats within a liquid filled clear glass tube. When the wooden case is flipped over, the sand within the hourglass flows down as the hourglass floats up. How does that happen? A perfect executive gift. Measures 9-1/8" x 3-1/2" x 1-7/8".