The Weather Notebook: Thermology

Thermology
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An interest in measuring air temperature goes back at least as far as ancient Greece, but the technology for an accurate and uniform thermometer was perfected less than 300 years ago. Hi, I'm Dave Thurlow for the Mount Washington Observatory and this is The Weather Notebook.

Galileo Galilei
Galileo made the crucial breakthrough leading to this essential invention. Drawing on classical texts that posited the expansion of air by heat and its contraction by cold, Galileo fashioned a device consisting of a glass bulb about the size of an egg attached to a long narrow glass neck. After heating the bulb in his hand, he inverted the open end of the neck in a basin of water; as the bulb cooled, he observed that water rose in the tube. Galileo "made use of this effect," in the words of a contemporary observer, "to construct an instrument for examining the degrees of heat and cold."

Word of Galileo's elegant contraption spread quickly through European scientific circles, and for the next hundred years scientists strove to improve on his design. One critical defect of Galileo's thermometer was that it was open to the atmosphere and thus fluctuated not only with temperature but with air pressure. This was resolved around 1640 when a sealed thermometer was developed under the direction of Ferdinand II, Grand Duke of Tuscany.

It wasn't until 1714 that a German-born physicist named Gabriel Fahrenheit succeeded in crafting a mercury thermometer that was not only sealed but fitted with a universal temperature scale based on fixed points. Fahrenheit assigned 32 degrees as the temperature for what he called "the commencement of freezing" and 96 degrees as the body temperature of a healthy person. Later, by lengthening Fahrenheit's scale, the boiling point of water was fixed at 212 degrees.

Using Fahrenheit's thermometer and the barometer that had been invented by an assistant of Galileo's in the 1640s, scientists could now ascertain both the temperature and pressure of air anywhere in the world. With these two tools, meteorology emerged at last as a modern science.

Thanks to today's contributing writer David Laskin. The Weather Notebook is underwritten by Subaru, the beauty of all wheel drive.