Ole Christensen Rømer was a Danish astronomer who, in 1676, made the first measurement of the speed of light and discovery that light travels at a finite speed. Rømer also invented the modern thermometer showing the temperature between two fixed points, namely the points at which water respectively boils and freezes.

Daniel Gabriel Fahrenheit FRS was a physicist, inventor, and scientific instrument maker, born in Poland to a family of German extraction. Fahrenheit invented thermometers accurate and consistent enough to allow the comparison of temperature measurements between different observers using different instruments. Fahrenheit is also credited with inventing mercury-in-glass thermometers more accurate and superior to spirit-filled thermometers at the time. The popularity of his thermometers led to the widespread adoption of his Fahrenheit scale attached to his instruments.