Hot & Cold: The Story of Temperature Scales

Today, checking the temperature is as simple as glancing at your phone. But for most of human history, "hot" and "cold" were purely subjective feelings. It took centuries of innovation, arguments, and three brilliant scientists—Fahrenheit, Celsius, and Kelvin—to give us the numbers we use today.

1593: Galileo and the Thermoscope

The journey began with Galileo Galilei. He didn't invent the thermometer, but the thermoscope. It was a simple glass tube consisting of a bulb of air and water. As the air warmed, it expanded and pushed the water level down. As it cooled, the water rose.

It was a brilliant start, but it had a flaw: it had no scale. You could see the temperature changing, but you couldn't measure it.

1724: Daniel Fahrenheit (The First Standard)

German physicist Daniel Gabriel Fahrenheit changed everything by inventing the mercury thermometer. Mercury expanded evenly and didn't stick to glass like water or alcohol.

To create his scale, he needed fixed points:

• 0°F: The freezing temperature of a brine (salt, water, and ice) mixture.
• 32°F: The freezing point of pure water.
• 96°F: Approximate human body temperature (he was slightly off; it's closer to 98.6°F).

Fahrenheit became the standard for the British Empire, which is why the US still uses it today.

1742: Anders Celsius (The Metric Revolution)

Swedish astronomer Anders Celsius wanted something simpler, based on the metric system (multiples of 10). He used pure water as his guide.

1848: Lord Kelvin (Absolute Zero)

While Celsius and Fahrenheit were great for weather, scientists discovered that temperature is actually a measure of molecular energy. If you cool something enough, eventually atoms stop moving entirely.

William Thomson (Lord Kelvin) calculated this point of "infinite cold" to be -273.15°C. He created the Kelvin scale starting at 0 (Absolute Zero). There are no negative numbers in Kelvin.

Why does the US still use Fahrenheit?

In the 1970s, the US Congress attempted to switch to the Metric system (Celsius) but faced public opposition. The main argument for Fahrenheit remains that it offers more "granularity" for weather (0-100°F covers the typical range of human experience better than -17 to 37°C).