Hot new tech of the 1700s: the thermometer

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“The hot new tech in the 1700s was the thermometer,” Brad Harris booms in his podcast How it Began. Tools of science “were necessary before the frontiers of knowledge could progress,” and the thermometer was no small example.

Robert Boyle used his family inheritance to fund experiments of the cold during the Scientific Revolution of the mid 1600s. [Emphasis on the cold; it’s amazing to think that <400 years ago we didn’t know how to define such everyday things.] Boyle first started studying water (hypothesizing that temperature was the movement of particles) and then moved to the study of air. In the early 1660s, using an air pump with a simulated vacuum built by his assistant Robert Hooke, Boyle published the relationship between temperature, pressure, and volume of a gas (ultimately: Boyle’s Law).

However, articulates Harris, Boyle was never quite satisfied with his findings because he didn’t have access to the proper tools. The thermometer had not yet been invented. He had to assume that temperature held constant in his air pump while identifying the inverse relationship between volume and pressure. But he had no way to be sure.

Sixty years later in the 1720s Daniel Fahrenheit invented the thermometer that we know today. He used mercury within hermetically sealed glass to hold pressure constant, allowing temperature and volume to fluctuate. Building on Boyle’s Law, Fahrenheit used his new thermometer to determine two fixed points: the lower fixed point was the coldest he could create experimentally (which he labeled 0° F) and the upper fixed point was the temperature of the human body (which he labeled 96° F). [See here for an interesting answer to why Fahrenheit might have chosen 96 vs. 100.]

Armed with this new scale and classification of “degree,” Fahrenheit then measured water’s boiling point (212° F) and freezing point (32° F).

In the 1740s Anders Celsius proposed a new measurement standard, using 100° C for the freezing point of water and 0° C for the boiling point of water instead.

Wait, you mean the other way around — right?

It wasn’t until a year after Celsius’ death (1945) that Carl Linnaeus (“father of modern taxonomy,” quotes Wikipedia) proposed switching the direction — such that today we use 0° C for the freezing point of water and 100° C for the boiling point of water.

Too often we forget about the history of the tools that were instrumental [ugh, puns] in propagating scientific knowledge and the compounding layer of additions that ultimately made (and make) them successful.


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