Put an ice cube in the beaker at the bottom.  Does the level of the water in the tube change?  Not clear, but looks like nothing happened.  Now put the ice cube on the glass container at the top.  You will get a decided change right away.  The water will rise.  Try heating the water at the bottom…nothing.  Now just put your hand around the flask at the top…the water goes down.

What’s going on here?  Why would the water go down, when you add heat?  It takes a moment, but then kids realize the thermometer is upside down.  That it is really “rising” when the water goes down.  Now another problem arises…what is the thermometric fluid? That is, what is the substance that is expanding and contracting with changes in temperature?  It’s the air above the water.  The water is just there so that we can keep track of the changes the air is going through.  This is a neat realization, and students suddenly appreciate the mechanics of thermometers in ways they hadn’t before.

Next, we take the temperature of different items.  We first mark where the water level is.  Then we take the temperature of our hands.  How far down did the water get pushed?  Curiously, it won’t be the same for everyone.  Most of the thermometers in the classroom are quite different from one another and even though there is no reason to think the air trapped in the bulbs is any different, how much they rise and fall is largely a function of the proportions of the glassware.  The one thing they have in common is the starting point: for each thermometer, that is room temperature.  But that means the next day, the base line may well have moved.  The room may be warmer and so the water would drop less with your hands.

What we need is a temperature scale that could standardize measurements.  That’s the problem Fahrenheit solved.

We all know that the Fahrenheit scale is marked by those curious numbers, 32° for the temperature of freezing water and 212° for the boiling point.  But who would make a scale that runs from 32 to 212?  No one.

Years ago I was in a small town in England on the North Sea, Aldeborough.  It was a typical Spring day, cold and damp.  After walking a while along the pebbly beach, Roy suggested we head into town for a cup of tea.  That sounded like a good idea, so we turned our backs on the water and walked up to the road that ran parallel to the shore.  As we crossed, I noticed it was 7th street.  I mention this because as we walked up the High Street the nest street was not 6th but 8th.  Who would lay out a town starting with the number 7?  No one.

I turned to Roy, our English friend and asked him what was up.  He smiled and asked me to look out into the inlet.  I was stunned to discover the tops of a couple of buildings quite a ways out into the water.  Aldeborough, an old town, was giving way to an encroaching sea.  First street was out there.

So, borrowing the morale of this tale, can we re-construct the rationale of the Fahrenheit scale?   It, too, was a centigrade scale.  Can you figure out what 0° Fahrenheit would have been?  Or 100°?