Anti-Gravity Reverse Sand Timers seem to defy gravity because the sand goes up instead of down. In reality, gravity is the reason the sand flows up. Each sand timer is filled with liquid. The sand weighs slightly less than the liquid inside, so the sand flows up as the liquid sinks down. The shape of each timer has a curve to it that makes it more interesting to watch than other timers. The sand runs for about 1 1/2 minutes. Approximate measurements: Height = 5 inches, Width = 3 1/2 inches, Depth = 1 1/4 inches.