Torricelli (1608 – 1647) proved that air pressure was subject to variations and in 1643 he devised the first barometer. Goethe, the famous German playwright, who enjoyed scientific experiments, later developed his own simple, but effective barometer using the principles established by Torricelli. This barometer is based on Goethe’s design. The Weather Ball Barometer will indicate changes in air pressure quickly and accurately. The ball is filled with colored distilled water. Once filled the air trapped inside the ball is no longer subject to variations in atmospheric pressure. The liquid in the indicator tube, however, remains open to the atmosphere and is directly affected by atmospheric pressure. When atmospheric pressure rises the liquid in the indicator tube is pushed down and an improvement in the weather can be anticipated. When air pressure falls the greater pressure inside the weather ball causes the liquid in the indicator tube to rise indicating that a deterioration in weather can be expected. Comes with full instructions. Height: 7.5" Ball Diameter: 4"