A sand timer is a centuries-old device that uses sand and gravity to measure time. In this ingenious G.W. Schleidt design, inspired by 17th century physicist Isaac Newton, the sand timer is suspended in a clear liquid within a glass cylinder. When the apparatus is inverted, the sand slowly trickles downward within the sand timer, while the timer itself slowly floats upward in the liquid. Measures 3-minute increments and contains purple sand; also available with magenta and blue sand. Overall height is 10 inches.