MARINE WEATHERGLASS This late-eighteenth century weatherglass was probably made in the province of Liège (Belgium). Originally it was an simple marine barometer. Glasses such as this were used on sailing ships well into the 19th century. The glassblower shaped the glass in such a way that, when filled, changes in the atmospheric pressure could be distinguished via the changing water level in the spout, and consequently weather changes could be forecast. How to read a weatherglass Slow upward movement of the water in the spout - this indicates a storm approaching within 8 - 24 hours, unless the storm changes direction Fast upward movement of the water - a storm is approaching and is already close by. If the storm changes direction, the water level drops quickly. The water flows out of the spout - a local storm is approaching at great speed and may break at any moment. Fast downward movement of the water level during a storm - the storm is nearly over. Steady water level, half-way up the spout - nice, stable water conditions. How to fill the glass and dye the water Take ordinary tap water and add some dye (red or dark blue, for example). Fill the glass through the spout until the levels in the spout and the reservoir are approximately the same, halfway up the glass. In warm weather the water may rise about an inch, but this has no forecasting significance. It is therefore best not to hang the glass in full sunlight or close to a heat source (radiator, stove, open fireplace, etc.).