Delisle scale

Delisle scale. The Delisle scale is a historical temperature scale invented in the early 18th century by the French astronomer Joseph-Nicolas Delisle. It is notable for being an inverted scale where higher numerical values correspond to colder temperatures, with its fixed points set at the boiling and freezing points of water. Although long obsolete, it saw significant use within the Russian Empire for nearly a century and represents an important, if curious, chapter in the history of thermometry.

History

The scale was created in 1732 by Joseph-Nicolas Delisle, a prominent astronomer at the French Academy of Sciences who had previously worked at the Paris Observatory. His initial motivation was to construct a thermometer suitable for low-temperature observations in astronomy and geophysics. Delisle's work was significantly influenced by earlier instrument makers like Daniel Gabriel Fahrenheit, whose Fahrenheit scale was gaining prominence. In 1732, Delisle was invited to Saint Petersburg by the newly established Russian Academy of Sciences, an institution championed by Peter the Great and later figures like Catherine the Great. He brought his thermometers to Russia, where they were adopted for meteorological and scientific observations. The scale was later refined, with the assistance of other academicians, to standardize its fixed points. Its use persisted in Russian territories, including regions like Siberia, well into the 19th century, outlasting its relevance in Western Europe.

Definition and conversion

The Delisle scale is defined by two primary fixed points: the temperature of boiling water is set at 0 degrees Delisle (°De), and the temperature of freezing water is set at 150 °De. This creates a scale that decreases as temperature increases, a design choice opposite to more familiar systems like the Celsius scale or the Kelvin scale. The division of the interval between these points into 150 equal parts means each degree Delisle represents a larger change than a degree on the Réaumur scale or the early Celsius scales. Conversion to the modern Celsius scale is achieved with the formula: °C = 100 - °De × 2⁄3. For example, a reading of 75 °De converts to 50 °C, while a common room temperature of about 20 °C corresponds to 120 °De. This inverted, descending numerical scheme was shared by the original Linnaeus scale but contrasts sharply with the ascending designs of the Rankine scale and the Newton scale.

Usage and legacy

The primary region of adoption for the Delisle scale was the Russian Empire, where it was employed extensively for scientific record-keeping throughout the 18th century. Notable figures who used or referenced it included the Swiss mathematician Leonhard Euler, who worked at the Saint Petersburg Academy of Sciences, and the explorer Vitus Bering, whose expeditions recorded climatic data. Its use is documented in the annals of the Russian Academy of Sciences and in correspondence between scientists across Europe, including those in France and Sweden. The scale began to fall into disuse with the increasing international dominance of the Celsius scale, especially following the reforms of the Metric system after the French Revolution. By the late 19th century, it was entirely obsolete, surviving only as a historical footnote in texts on the history of science. Today, it is occasionally referenced in discussions of obsolete measurement systems alongside scales like the Rømer scale.

Comparison with other scales

The Delisle scale is most directly comparable to other early temperature scales developed in the same era. Unlike the Fahrenheit scale, which set its zero point using a brine mixture, or the Réaumur scale, which used an 80-degree range between fixed points, Delisle's design was uniquely inverted. It shared this descending characteristic with the original Linnaeus scale used in Uppsala. When compared to the modern International System of Units base unit, the Kelvin scale, which starts at absolute zero, the Delisle scale appears arbitrary. Its 150-degree range between phase changes of water was similar in span to the 100-degree Celsius scale but less finely graduated. The scale's persistence in Russia contrasted with the quicker adoption of the Celsius scale in nations like Sweden and France, highlighting how scientific standards can remain regional. Other contemporary scales, such as the Leiden scale used for cryogenics or the Wedgwood scale for high temperatures, served more specialized niches, whereas Delisle aimed for general meteorological use.