Re: PARADE & Marilyn

[Gary Karshner <karshner@STMARYTX.EDU>]

> 2)  How was the lower end of the scale chosen?  I have heard her 
> answer, that he arbitrarily set 32F = freezing, and that he chose 0F as 
> the lowest freezing point of salt water.  Anybody have an informend 
> opinion on the true history of the Fahrenheit Scale.

Tim, 
        If memory serves, zero was chosen as low as you make an ice salt
mixture go. Remember that negative numbers were less then 100 years old and
not generally used, so he wanted to avoid them by taking zero as the coldest
temperature you could make in the laboratory. In the 1760's there were
reports that mercury froze in thermometers in Canada, they were recorded as
negative 40 degrees F, but that is the first reference I can point to of
negative temperatures although must be other earlier references to them. 
        Fahrenheit also wanted to make human body temperature 100, but found
that he could more reliably use boiling water, and ice water to calibrate
his instruments. Fahrenheit's great contribution was thermometers that could
be calibrated and reliability kept that calibration. Earlier thermometers
were good only for relative measurements. Galileo used one that had a bulb
of air on one end and a glass tube stuck into water. The level of the water
would rise and fall as the temperature changed, but changes in barometric
pressure and evaporation would obviously affect it as well.

Gary
Gary Karshner

St. Mary's University
San Antonio, Texas
KARSHNER@STMARYTX.EDU