Diagram of a thermometer similar to
the one describe by Leurechon, c. 1638.
Note that hotter temperatures have
smaller magnitudes degrees associated with
them. Image from Wellcome collection,
used under CC license.
This post is in part inspired by my current location (the Vatican Observatory outside Rome, staffed by Jesuit scientists) and in part by a piece I wrote earlier this year for Nature Chemistry (Changing chemistry by degrees).
The word thermometer was first coined (in French) in a book of mathematical recreations written in 1626 by Hendrik van Etten, the pen name of Jesuit Jean Leurechon. It's also an early example of adding a scale to a thermometer, though there's a long way to go before anyone will have a reproducible scale such as those we take for granted today.
Such thermometers, he (correctly) predicts will be practical instruments, as they might be used to monitor the temperature of a room or a furnace, to record the weather and to measure fevers in the ill.
One oddity about the thermometer described is that a reading of 9 degrees was colder than that of 2 degrees, the liquid dropped in the tube as things warmed up.
A century later, Anders Celsius constructed a temperature scale based on water's phase changes which ran in the same direction. Water on Celsius' scale boiled at 0 degrees and froze at 100 degrees. This reverse run didn't last long, two years later Carl Linnaeus (of taxonomic fame) used the scale to describe conditions in a greenhouse, but flipped it to the form in which we know it today, where 100 is the boiling point of water.
It is tempting to think that Celsius' scale ran in the direction it did because it mimicked the scale used by Father Leurechon. But Fahrenheit's scale, which preceded Celsius' by two decades, runs in the modern direction, higher temperatures are hotter.
This also parallels the classic notions of degrees of heat in play during the medieval period. There were four (or eight or six, depending on the source) degrees of heat, the first being more or less physiological temperature, the fourth being a blazing hot furnace.
Read the version for science-sorts at Culture of Chemistry.