The Celsius scale is the standard unit of temperature measurement used globally, but the older term “centigrade” still appears in common conversation and historical documents. This dual terminology stems from a history involving an inverted scale, a descriptive name, and a conflict with international measurement standards. The shift to “Celsius” was a deliberate decision to eliminate ambiguity and formalize temperature measurement within the global scientific community.
The Original Centigrade Scale and Its Inventor
The term “centigrade” literally describes the scale’s fundamental design, deriving from the Latin words centum (“100”) and gradus (“steps” or “divisions”). This name reflects the 100 divisions placed between the freezing and boiling points of water, which served as the scale’s original fixed points. Anders Celsius first proposed this 100-step temperature scale in 1742.
Celsius’s original design was the reverse of the scale used today. He set 0 degrees as the boiling point of water and 100 degrees as the freezing point. Shortly after his death in 1744, the scale was inverted, notably by the botanist Carl Linnaeus, establishing 0 degrees at the freezing point and 100 degrees at the boiling point. Although the orientation changed to the modern standard, the descriptive name “centigrade” remained popular for nearly two centuries.
The Conflict with Metric and Angular Measurements
The widespread use of “centigrade” created a problem for international scientific communication. As the metric system (SI) became standardized globally, precise and unique terminology for measurements grew increasingly important. Scientists discovered a semantic overlap because “centigrade” was already used in other technical fields, specifically for angular measurement.
In French and Spanish, “centigrade” denoted one-hundredth of a gradian (or grade), a unit of plane angle. A gradian divides a right angle into 100 grades. This created confusion, as “centigrade” could ambiguously refer to either a temperature measurement or a small unit of angular measurement. Eliminating this duality became a priority for international standards bodies working to establish a globally uniform system.
Formal Adoption of the Name Celsius
The resolution to this naming conflict occurred in 1948 at the 9th General Conference on Weights and Measures (CGPM). The CGPM, responsible for the global standardization of measurement, formally adopted the designation “degree Celsius” to replace “degree centigrade.” This decision honored the scale’s original inventor, Anders Celsius, and eliminated the ambiguity with the angular measurement term.
By naming the unit after its originator, the CGPM aligned the temperature scale with other major units, such as the Kelvin and Fahrenheit scales, which are also named after their creators. Although “centigrade” is technically obsolete in official scientific contexts, its long history means it persists in historical texts and is sometimes still used in casual language. The official change solidified “Celsius” as the internationally recognized term for temperature.