The Centigrade Scale: Why It's Not Liked

Let's face it. The experiment during the past decade to entice Americans into accepting the metric system was a flop. Most items such as a loaf of bread or a bottle of wine now carry metric equivalents in grams or liters on the label, but the general public still buys (and most products are still most prominently labeled) in pounds or gallons.

The same can be said for the centigrade (or Celsius) temperature scale. People don't like it. At first glance, it would appear that, with zero set at the freezing point of water at sea level and 100 at the boiling point, the centigrade scale is logical and obvious.

To advocates of the Fahrenheit scale, however, it is the selection of water as the definitive medium which is precisely the point of contention. Mr. Ian B. Patten of Anchorage, an outspoken critic of the metric system who laments the changeover to metrics in Canada (from whence he hails), observes that, while the centigrade scale may be preferential for scientists working in laboratories, the Fahrenheit scale is more suitable for measuring air temperatures to which we are all subject.

Quoting from a letter I received from Patten: "Fahrenheit grouped all earth's moderate temperatures between 0 and 100 degrees. How accurate he was is shown by today's extremes of -128 and +136 being virtually equidistant from zero. There is a similar balance in the equatorial regions of the moon of -280 and +260F. Average temperature worldwide is 58 degrees F. Isn't it logical and natural to record hot days in the 80s and 90s instead of the high 20s and low 30s? As a water scale masquerading in air, Celsius sacrifices double the accuracy of Fahrenheit with its too-widely-spaced gradations geared to water."

In another letter, Patten again draws a distinction between a scale suitable for water temperatures and one used to measure air temperatures. He writes: "Celsius gives us a general extreme range of air temperatures from -50 to +50, leaving the top half of the positive scale virtually untouched. With Fahrenheit, earth's average air temperatures range from 0 to 100 degrees, as they should with any true air-oriented scale."

Agree or disagree, you have to admit that Patten makes a pretty good point. Of course, Europeans (and most of the rest of the world) raised with the metric system think that warm days in the 20s and 30s are perfectly natural.

Also, although it may seem reasonable, it's not clear if Fahrenheit really based his scale on climatic considerations when he designed it in the early 1720s. His "high" temperature was arbitrarily set at 96, both because it is easily divisible, and because it is roughly the body temperature of a human. His "low" temperature of 32 was set at the freezing point of a mixture of water, salt and ice. With these two points defined, he could extend the scale upward to find that water boiled at 212 degrees.

Intentionally or not, Fahrenheit was pursuing roughly the same line of reasoning that had been followed by experimenters in Florence a century earlier. Workers at the Accademia del Cimento had chosen the cold of winter and the heat of summer as their high and low points. By cold of winter they meant the temperature of snow or ice in the severest frost. For the heat of summer they used the temperature of a cow or deer. However, it remained for Fahrenheit to describe these values in terms that could be defined by the expansion of mercury in a tube.

There is no question that, for scientific purposes, the Celsius scale (defined by Anders Celsius of Sweden in 1742) is far superior. The Fahrenheit scale would make little sense in, say, interplanetary exploration, and it is cumbersome to use for the extreme high and low temperatures encountered in the laboratory.

However, the general public, at least in North America, seems to overwhelmingly prefer the Fahrenheit scale for everyday use. It would be interesting to know if this is merely because it is the scale that most of us have grown up with, or if it is because the zero to 100 range more closely relates to the extremes of seasonal air temperature. On the surface, it would appear that the majority of people don't feel much differently about it than the Florentine scientists did in the 1600s. Cold snow and warm cows still represent two temperatures to which we can relate.