----- Original Message -----
Sent: Friday, 2005-07-29 17:32
Subject: [USMA:33759] BOILING, FREEZING
AND THE FAHRENHEIT THERMOMETER
Might be interesting to
someone...
Nat
2005 The Buffalo News
Buffalo News (New York)
May 8, 2005 Sunday
FINAL EDITION
SECTION: SCIENCE/ENVIRONMENT; NATURE WATCH; Pg. I6
LENGTH: 728 words
HEADLINE: BOILING, FREEZING AND THE FAHRENHEIT THERMOMETER
BYLINE: By Gerry Rising
BODY:
We have come to
accept some rather strange numbers as part of our culture. Thus, on the
Fahrenheit scale, which we still use in this country, we have 32 degrees as
the temperature at which water freezes and 212 degrees as the temperature at
which it boils. Why those particular numbers? Are they just two more values to
make school science tests difficult?
Clearly, the
Celsius scale, with water freezing at 0 degrees and boiling at 100 degrees, is
easier to remember, but my concern here is not promotion of the metric system. It doesn't need my support. Rather, I will
explore the history that led to those numbers on the Fahrenheit scale. I was
led to this history by a former student, Dipendra Bhattacharya, now a
professor at Clarion University of Pennsylvania. He was asked why those
numbers were chosen and passed on the question to me. I found the answer in H.
Arthur Klein's 1974 book, "The World of Measurements," and I summarize his
answer here.
Turn back the calendar over 300 years,
and you will find that there were very few instruments for measuring
temperature. Then in about 1700, Danish astronomer Ole Roemer, already famous
for his proof that light travels at a finite speed, not instantaneously as had
been believed, turned his attention to this problem.
Roemer constructed rudimentary thermometers much like those we use
today: glass tubes in which alcohol expanded. He was then faced with the
problem of how to associate a scale with the rising liquid.
A few years earlier Italian scientist Carlo Rinaldi had proposed that
any scale should reflect the freezing and boiling points of water, but Roemer
thought that two other temperatures should be taken into account. These were
our body heat and the lowest temperature of a mix of water and ice he could
attain in his laboratory. He reached this lower temperature by adding salt to
the mixture.
So now Roemer had four scale points. He
chose 0 degrees to represent that "lowest" temperature and 60 degrees to
represent boiling. Why he chose 60 is unclear, but it is a number that appears
in minutes and seconds of time and in angle measure. In his rudimentary scale
this gave Roemer 7.5 degrees for ice freezing and 22.5 degrees for body
temperature.
Enter German scientist Daniel Gabriel
Fahrenheit. He adapted the idea of Ismael Boulliau to use quicksilver, which
we now know as mercury, in his higher quality thermometer tubes. As Klein
says, "Had it not been that his thermometers were so sound and practical, the
Fahrenheit scale that he devised for them would never have become widely
known. As it is, and rather ironically, too, Fahrenheit is famous today
chiefly because of that same peculiar and highly illogical scale, whereas many
of his more substantial contributions to scientific measurement are seldom
mentioned."
Taking advantage of the greater accuracy
of his mercury thermometers, Fahrenheit decided to expand the Roemer scale by
multiplying its values by four. Thus his four scale points were: 0 degrees,
low; 30 degrees, ice; 90 degrees, body temperature; and 240 degrees,
boiling.
Those are, of course, far nicer values than
those he finally adopted. Unfortunately, he found that they didn't quite
serve, and he began to tinker with them. First, he found the body temperature
too low and he changed it from 90 to 96 degrees, as accurate as he could make
it but still not the 98.6 degrees we use today. This change, however, raised
the freezing point of water to 32 degrees, its present value and the answer to
the first part of our problem.
The boiling point,
too, had to be changed. It had not been all that accurately placed on the
Roemer scale because the alcohol used in thermometers boils at a lower
temperature than water.
So Fahrenheit had to adjust
his scale one more time. He reduced his 240 degrees to 212 degrees to fit with
his other measures, finally arriving at the three scale points that continue
to determine for us Fahrenheit temperatures: 32 degrees, water freezing; our
corrected 98.6 degrees, body heat, and 212 degrees, water boiling -- all at
sea level, of course. That 0 degrees that provided the scale's starting point
is long forgotten.
Klein calls the Fahrenheit scale
bizarre, and I cannot disagree. One defender, however, notes that for weather,
it serves quite well, our expected temperatures ranging approximately between
0 and 100.
e-mail: [EMAIL PROTECTED]
GRAPHIC: Associated Press We measure the outdoor
temperature using the Fahrenheit scale.
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