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Hygrometer: Leonardo da Vinci's Weather Predictions
Using a hygrometer you can measure the humidity in the air, which can help you predict weather changes. In Leonardo's time, meteorology (the science of the earth’s atmosphere and weather) was far from well-developed. No local weather forecasters existed to tell you that the next few days would be cloudy, or tell whether the winter would be harsh or mild.
Instead, in the Renaissance, people relied on ancient Greek knowledge, and especially that of the Greek philosopher Aristotle, to better comprehend the weather and the earth’s atmosphere.
Aristotle's Meteorologica (Understanding of the Weather)
The term meteorology was first used by Aristotle in 340 BCE, when writing a book on his theories about the natural world, including rain, clouds, snow, hail, thunder and lightning, and climate. It was only natural for Aristotle to employ the title Meteorologica because in ancient Greece, anything that fell from the sky or was suspended in the sky (such as mist or fog) was called a meteor.
In Meteorologica, Aristotle detailed various aspects of weather and climate that scientists still study today, things like how lightning is caused, why different areas have different amounts of rainfall, where winds come from, and the correlation between the height of clouds and the amount of rainfall they bring. Aristotle’s observations about weather and climate were often accurate and detailed.
For instance, in Meteorologica, Aristotle describes hail:
Hail is ice, and water freezes in winter; yet hailstorms occur chiefly in spring and autumn and less often in the late summer, but rarely in winter and then only when the cold is less intense. And in general hailstorms occur in warmer, and snow in colder places.
One issue Aristotle’s Meteorologica had was the fact that when he tried to explain what caused the weather he observed he was usually wrong. All of his explanations rested on the false assumptions that the earth was the center of the universe, and that the elements of fire, water, air, and earth made up everything in the world, including weather.
Despite the fact that he was wrong, Aristotle's ideas about weather and climate were widely accepted as truths set in stone for more than 2,000 years. After all, anyone could observe the way water circulated through the earth and its atmosphere simply by watching it rain or snow. However, since water vapor is invisible, no one could fully comprehend its properties.
It was only in the course of the Renaissance that people started to think more about the natural world and the various aspects of weather and climate that were invisible to the naked eye. The question is, 'Could people predict if it was going to rain?' Did they wonder what caused the air to feel so heavy in the sizzling heat of the summer when there weren't any clouds in the sky?
Nicholas of Cusa's Hygrometer
In 1450, Nicholas of Cusa, a German cardinal and mathematician, was the first person in history to conceive a weather device, when describing a hygrometer, an instrument that could be used to measure the amount of moisture in the air. He had the following idea:
If someone should hang a good deal of wool, tied together on one end of a large pair of scales, and should balance it with stones at the other end in a place where the air is temperate it would be found that the weight of the wool would increase when the air became more humid, and decrease when the air tended to dryness.
We have no evidence that should suggest Nicholas of Cusa ever built his hygrometer, but Leonardo did. In 1481, he took the description and used it to put together his own hygrometer.
Leonardo da Vinci's Hygrometer (Video)
Quick Steps to Make a d Vinci Style Hygrometer
Here’s an easy way to measure the amount of humidity in the air.
- Cut the tops off the milk cartons so you have two equal-sized containers.
- Melt a thin coating of wax on the bottom of one container.
- Poke holes in each side of the containers and thread string through them.
- Tie the string ends to the ends of the coat hanger, so one container is at each end.
- Put some cotton balls or a sponge in the container without the wax coating.
- Hang the hanger outside where it won’t be affected by wind, then add more cotton or pieces of sponge to the second container so that the two containers are level and balanced.
- Leave your hygrometer outside, checking it every ten minutes to see if the container with the cotton or sponge has grown heavier than the container with the wax.
- If the container with the sponge or cotton balls has grown heavier, it means the humidity level of the air is rising - the higher the humidity, the more water vapor in the atmosphere.