Barometers Realm

A truly unique feature of this piece is its brass top. Not only does it enhance the glass’s aesthetic appeal, giving it a distinctive character, but it also serves a practical fastening function. The brass rim with decorative cutouts in the form of stylized Gothic elements lends the piece particular elegance, while the heavy suspension loop suggests that this thunder glass was designed to be hung in an interior setting. Such a combination of glass and metal is exceptionally rare, indicating that this is not merely a household object but a masterpiece of craftsmanship.

Typically, thunder glasses are filled with water, the color of which can be chosen at will. The reservoir also contains a fixed amount of air, as it is hermetically sealed except for the spout. When atmospheric pressure rises, the water level in the spout drops, and the air inside the reservoir compresses slightly. Conversely, when pressure falls, the air in the reservoir expands, pushing the water level in the spout upward. In the case of a sudden drop in pressure, such as before an approaching storm, the water level in the spout may rise so high that it dramatically spills over the edge.

This is an early type of thermo-barometer, dating back to the first decades of the 17th century, and it is considered a distinctly Dutch invention. In this context, history remembers two names: Cornelis Drebbel and Gijsbrecht de Donckere. Cornelis Drebbel entered history as a rare kind of Renaissance master-universalist: a glassblower and lens-grinder, musician, engraver, and draftsman — a man for whom craft was not a supporting trade but a direct path to experiment. His youth coincided with an era when seafaring demanded new ways of “reading” the world: the compass was still scarcely mastered, there were no precise clocks on board — only sandglasses — latitude calculations were often wildly inaccurate, and an instrument that could foretell an approaching storm was little more than a wish. Drebbel grew within this practical demand, moving with equal confidence between chimneys and furnaces, his Perpetuum Mobile, optical lenses, fountains, automata, and experiments with the “new spirit” (oxygen). His reputation crossed borders: London and the court of James I, demonstrations at Whitehall, and then Prague under Rudolf II, where the emperor valued not only spectacle but a continuous stream of engineering ideas.

It is precisely along this line — from the Perpetuum Mobile to the “weather glass” — that the prehistory of the Donderglas begins. Working with glass and sealed volumes of gas, Drebbel observed how a liquid column in a narrow tube responded not only to heating and cooling, but also to disturbances in the air: a gust of wind, the slam of a door, the approach of bad weather. His contemporaries already linked such “glass weather instruments” with the ability to predict storms — long before Torricelli’s mercury barometer. Within this tradition, the “bottle” form took root, where pressure, temperature, and the liquid column interplay — a principle later refined into a more coherent and reproducible instrument by another Dutchman, Gijsbrecht de Donckere. At his initiative, such weather glasses were produced and sold in large quantities. They were used especially by coastal residents and fishermen.

Unfortunately, thunder glasses are also affected by temperature fluctuations. If the temperature rises, the air inside the reservoir expands, causing the water in the spout to rise even if atmospheric pressure remains unchanged. Conversely, cooling causes the water level to drop. Thus, a donderglas functions best in environments with relatively stable temperatures, where changes in water level are primarily influenced by fluctuations in atmospheric pressure.