Tuesday, June 12, 2012

The 32 Degrees of Frost

They turn out to be an interesting, indeed an amusing, subject—in the general category of “Everybody knows it but virtually no one knows why.”

The beginnings of thermometers go back to what might as well be the dawn of time, at least from our ignorant perspective. We live in a scientific age, but it’s not the first one. Early in the Hellenistic era (which began, let’s say, with the death of Alexander the Great, 323 BC), Philo of Byzantium (circa 280-220 BC) discovered that air increases in volume when heated, decreases when cooled, and to demonstrate this he used a little glass tube sealed at the top. He put the open end into a jar of water. A little of the water came up into the tube. As the air got hotter, the water level in the glass went down; as it got colder, the water rose. Then, early at the beginning of our scientific age, several people, who knew of these discoveries, repeated the experiment, among them, most notably Galileo Galilei (1564-1642). He called his device a thermoscope.

These early devices, of course, had no scale. The indicator inside them would go up or down, but no little lines, with numbers, to mark where they stopped moving. That began in the seventeenth century with the Danish physicist Ole Rømer (1644-1710). There is no Rømer scale today, but Daniel Gabriel Fahrenheit (1686-1736), a German, started with Rømer’s. Rømer, however, is not forgotten. His fame is linked to measuring the speed of light. Rømer set the bottom of the scale at the temperature of brine—thus a mixture of water, ice, and salt. This sort of mixture is colder than frozen water. This was Rømer’s 0° of temperature. Water froze at 7.5°, the human body’s temperature was 22.5°—we’re still talking about Rømer’s own scale. But here is where Fahrenheit started. He too began with brine—rather than the temperature of water ice.

Fahrenheit reasoned as follows. It’s hard to work with fractions—like 7.5 and 22.5. Therefore he multiplied each by four: 30 and 90. Zero times 4 was, of course, still zero. Fahrenheit set about to mark his glass tube. It was a little hard to do. He had another idea. He decided to set the freezing temperature at 32 and the body temperature at 96—and this for entirely practical reasons: ease of marking. The difference between death and life, as it were—frozen stiff and throbbing with heat, was 64 degrees. But 64 is 2 to the sixth power, so Fahrenheit found it easy to mark his glass tube. He divided the area between 32 and 96 by six equal length. Later work by others showed that water actually boils at 180 degrees above its freezing point. This introduced slight modifications to the Fahrenheit scale—so that the human body temperature came to be adjusted to 98°.

Physical substances actually reveal temperature. The scale added is arbitrary. Anders Celsius (1701-1744), a Swedish astronomer, decided that the boiling point pf water should be 0 and the freezing point 100. But this got turned on its head later on—so that now we boil water at 100° C and freeze it at 0° C.

The genuinely scientific measurement of 0° came with a man born as William Thomas (1824-1907); later he was ennobled and became Lord Kelvin, therefore the Kelvin scale. Kelvin thought that 0 should be reserved for the absolute absence of any temperature. This turns out to be at -459.67° F and ‑273.15° C. I first met 0° K when, in my youth, I did my first serious study of cryogenics while working for an engineering company—and discovered that there was life beyond Celsius. Rømer, Fahrenheit, Celsius, Kelvin; that’s the order in which our scales appeared. But who is next. And where will this person start. With brine? While watching a pot boil? While holding a thermometer into a nuclear explosion? Or focused squarely on the body’s temperature, as Rømer and Fahrenheit were? Such thoughts arise when the temperature outside is the same as the temperature inside—and I am miserable enough to start thinking, again, about central air.
Illustration courtesy of Wikipedia commons (link).

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