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Centigrade vs. Fahrenheit
In the United States part of North America, where I
live, we are slowly but surely switching from the system of English measurements (feet,
miles, cups, gallons, etc.) to the metric system. While I have no quarrel with the
use of metric for weights and measures, I do not like the conversion from Fahrenheit to
centigrade to measure temperature, and I will tell you why.
My aversion to centigrade is based in my experience
of using it to measure air temperature, and that is what I will discuss. This usage is
what most of us encounter daily. When we come to measuring temperature for some
other purpose, such as medicine, industry, even cooking, I think that any scale is
basically as good as another, since we rely on gauges and meters to set and measure
those temperatures, and not on our direct experience of temperature.
Metric measures of length, volume and weight are
easily applied in everyday life and have clear advantages over the hodge-podge of
English measurements, but Fahrenheit used in everyday life shows no liabilities and
centigrade no advantages over it. The only reason to adopt centigrade over Fahrenheit
is the mistaken belief that it is more consistent with metric measurements of
physical quantities. In fact, I consider the Fahrenheit scale to be superior to the
centigrade scale for the following reasons:
- The Fahrenheit scale is more tuned to human experience, especially at its lower end.
In my part of the world, temperatures in winter often drop below freezing. An air
temperature around or a little below freezing is consequently no big deal. However,
temperatures below 0°F are relatively rare, and definitely feel like a bigger
deal than merely freezing. The Fahrenheit scale reflects this experience: most winter
temperatures can be expressed in positive values, and values below 0°F are exceptional
and remarkable. I can go out to get the paper in my nightclothes at 32°F, but I put on
my coat and hat at -1°F. The centigrade scale, on the other hand, reaches 0° at
temperatures that feel relatively benign, and must resort to negative values far
sooner. Once in the negative values, centigrade loses all human perspective. There
is little difference on paper between -1°C and -20°C, but the physiological and
psychological differences are profound. In other words, values below 0° have more
meaning and more psychological weight in the Fahrenheit scale than they do in the
centigrade.
- The Fahrenheit scale is more precise than the centigrade. There are 180 divisions
between the freezing and boiling points of water in the Fahrenheit scale, but only 100
in the centigrade; thus, the Fahrenheit scale is almost twice as sensitive as the
centigrade. One must resort to fractions of a degree centigrade to approach the
precision Fahrenheit offers in whole degrees. In the everyday world of human experience,
this never happens: the weatherman gives the temperature centigrade in whole numbers,
bank time-and-temperature displays show whole numbers, etc. Therefore, users of the
centigrade scale routinely are subjected to less precise measurements of temperature.
And this is no trivial matter: a single degree of change (in °F) on one's home
thermostat can make a significant difference in the temperature of one's home
(and the crankiness of one's spouse!). I've never seen a centigrade thermostat that
measured in fractions of a degree, so users of those thermostats have lost almost
half of their ability to regulate their home's temperature.
- The centigrade scale is unnecessary. Metric measures of
distance, weight, etc., are simple and logical. Since they are based strictly on powers
of ten, it is very easy to convert units to smaller and larger units, which, of course,
is done all the time. This to me justifies their existence; I still don't know, for
example, how many ounces are in a pint, although I've used them all my life. But
temperature is never expressed in larger or smaller units. The degree is the only
measure of temperature there is. There is never a need to translate a given
temperature into some larger or smaller unit, so the advantages of conversion found
in a decimal scale
are unnecessary. If fractions of a degree are needed (in science or industry), it is
no more difficult to divide a Fahrenheit degree into tenths than it is a centigrade
degree, since there is no need to ever group these units into anything larger than a
whole degree.
Moreover, the various measurements of weight, volume and length can be defined in terms
of each other (eg. a gram is the weight of one cubic centimeter of water), so it is
logical to use a commensurate scale to express them. But temperature has no logical
relationship to these other measurements, is not defined in their terms, and has no
need to follow the same type of scale.
- The centigrade scale is arbitrary. The usual criticism of the Fahrenheit scale
is that it has no logical benchmarks, compared to the logical
(one might even say inevitable) choices of the centigrade scale: benchmarks at the
freezing and boiling points of water, with divisions made using powers of ten. Yet
there is nothing inevitable about any of those choices. The decision to use a power
of ten to divide the scale is entirely arbitrary. As I noted above, the temperature
scale has no real connection to any other scale, and the selection of 100 divisions was
made not from logical necessity but from a desire to mimic the divisions of the other
metric scales and thus appear more "scientific". The selection of the freezing and
boiling points of water as the benchmarks of the system are also arbitrary. In fact,
the choice of water to mark the benchmarks is arbitrary. To be strictly logical,
0° should be absolute zero, the cessation of all molecular motion, and we should be
measuring in degrees Kelvin. Of course, no one would ever do this, because the
Kelvin scale is too far outside human experience. But I would argue that the
Kelvin scale is the only truly logical scale, and as soon as we make
concessions to human experience and ignore it in favor of centigrade, we have admitted
that the centigrade scale is no less arbitrary than any other scale.
So, I hope I have convinced you that the centigrade
scale is not markedly superior to the Fahrenheit, in fact is inferior in several
ways. It has been
promoted only because it seems more logical and "scientific" than the Fahrenheit
(and perhaps because of ancient rivalries between German and French scientists).
Since there is no fundamental relationship between the measurement
of quantity and the measurement of temperature, there is no reason why metric scales
for quantities and Fahrenheit for temperature can't co-exist.
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