Weather Whys; Galileo and Temperature

This is weather-wise. Air temperature is often one of the first things we think of when we consider the weather, and for centuries man had only the evidence of his senses to give him an indication of what the temperature was. The weather instrument we know as the thermometer came into being in the mid-17th century, but the astronomer Galileo discovered the basic principle behind it around the year 1600. To illustrate that principle, think of the familiar glass tube thermometer with the silver or red liquid in a small ball but one end. The liquid rises in the tube when the temperature is warmer and sinks when the temperature is cooler. That's because the liquid expands when it's warmed. Since the tube is sealed, the liquid has nowhere to go but up the tube. And in the same way, it contracts and sinks when it's cooled. Galileo demonstrated that principle with an empty flask and a pan of water. He warmed the flask then turned it upside down and placed it in the water. The air inside the flask contracted as it cooled and watered from the pan rose inside

the flask to fill the space left by the contracting air. Galileo recognized the value of his new discovery and set about trying to link the level of water in the flask to the temperature in the room. But that didn't work for him because his device had problems. First the pan of water was open to the air so the weight of all the air above the pan was pushing down on the water. As a result, changes in air pressure had a lot more to do with the water level than the air temperature did. That's why modern thermometers contain their liquid in air-tight tubes. Also, Galileo's device used water which made it useless for measuring temperatures below 32 degrees Fahrenheit. Mercury and alcohol freeze at much lower temperatures and that's why they're often used in many of today's thermometers. For weather-wise, I'm Drew Barlow.