Magna Carta, signed reluctantly by bad King John in 1215, contained in medieval Latin a clause which required that "throughout the Kingdom there shall be standard measures of ale, wine and corn; dyed cloth, haberject and russet shall also be produced to a width that shall be fixed, and weights are to be similarly standardised."
The barons, however, were less successful when it came to scientific matters. Even by 1665, Robert Boyle felt it necessary to complain: "We are greatly at a loss for a standard way whereby to measure cold. The common instruments show us no more than the relative coldness of the air, but leave us in the dark as to the positive degree thereof; whence we cannot communicate the idea of any such degree to any other person."
In the following 100 years, however, at least 35 different scales of temperature were suggested. In 1724 Daniel Fahrenheit devised the widely-known scale that bears his name, and in the 1742 Anders Celsius proposed the one we use today.
But between the years 1641 and 1780 at least 35 different scales of temperature were proposed and introduced to limited use. Indeed, in those days anyone who constructed a new type of thermometer seemed to throw in a new scale of temperature for good measure.
The proliferation is illustrated by a device to be found in the Royal Maritime Museum at Greenwich, which consists of a circular plate with a pivoting arm, described as "A General Thermometer". Manufactured about 1720, it is engraved with 16 different thermometer scales, and provided an easy means of converting a reading from one temperature scale into any of the other 15.
Most of the scales on the General Thermometer are quite unfamiliar to us now. The Fonlex Scale, for example, had a freezing point of -33 (minus thirty-three) degrees and a boiling point of 245; on the Paris Scale the corresponding points were 24.5 and 238, on the Cruquis 106 and 151, and on the Edinburgh Scale, eight and 47.
Two of the featured scales were constructed in such a way as to give diminishing numbers for increasing temperatures: the Royal Society Scale had a freezing point of 79 and a boiling point of -170 (minus one hundred and seventy degrees), and the De Lisle ranged from 150 down to zero.
Other temperature scales engraved upon the instrument include La Hine, the Hales, two scales devised by Rene Antoine de Reaumur and two described as "Florence", together with the Nenton, Amenton and Poleni Scales and, of course, the Fahrenheit.
Celsius, alas, is missing; his scale did not come into common use until 20 years after the manufacture of this useful "General Thermometer".