Anders Celsius put boiling at zero and freezing at one hundred
When Anders Celsius proposed his temperature scale in 1742, water boiled at zero degrees and froze at 100. The scale carrying his name today runs the other way round. That reversal is one small twist in the long, tangled history of an instrument that no single person can honestly be said to have invented.
The roots go back to antiquity. In the 3rd century BC Philo of Byzantium joined a sealed hollow sphere to a tube dipped in liquid: heat the sphere and air bubbled out, cool it and liquid climbed the tube. Hero of Alexandria described a sun-driven fountain on the same principle, and Galileo had read that work by 1594. The physician Galen supplied two key ideas, degrees of hot and cold, and a reference point made by mixing ice with boiling water.
Galileo and Santorio Santorio built air-filled bulbs over columns of water, but without markings these were thermoscopes, showing only whether things were warming or cooling. Adding a scale is what makes a thermometer, and Santorio published the first such drawing in 1625. Although Galileo often gets the credit, no document shows he ever made one. Jean Leurechon first used the word, in French, in 1624, joining Greek terms for warmth and measure.
Those early devices doubled as barometers, reacting to air pressure. Around 1654 Ferdinando II de' Medici, Grand Duke of Tuscany, produced a sealed liquid thermometer immune to that problem, yet every maker still used his own scale. Christiaan Huygens suggested in 1665 fixing graduations to ice melting and water boiling, and Isaac Newton in 1701 proposed 12 degrees between ice and body heat. Daniel Gabriel Fahrenheit swapped alcohol mixtures for mercury in 1714 and offered his scale a decade later.
Medicine adopted the tool slowly. Herman Boerhaave was the first doctor to take readings in clinical practice, and in 1866 Thomas Clifford Allbutt designed a clinical thermometer that gave a result in five minutes rather than twenty. The official International Temperature Scale of 1990 now stretches from 0.65 kelvin to about 1,358 kelvin.
Source: Thermometer
