During the early 1700's, the Admiral Fitzroy was used by sailors to forecast weather for nearly 250 years. They relied upon the constantly changing crystal formations to predict the weather. It is believed that the electromagnetic changes in weather patterns activate the crystals inside. This storm glass is 6" tall and can be used alone on a desk. How to Predict the Weather: If there are large flakes throughout the liquid, it will be overcast in temperate seasons or snowy in the winter. If there are threads near the top, it will be warm or windy. If the liquid contains small stars on a sunny winter day, then snow is coming. If there are crystals at the bottom, this indicates frost. A cloudy glass with small stars indicates thunderstorms. If the liquid is clear, the weather will be bright and clear.