The history of the barometer (and how it works) - Asaf Bar-Yosef

Summary

This script explores the evolution of the barometer, beginning with Aristotle's belief that a vacuum couldn't exist. For nearly 2,000 years, this idea went unchallenged until the 17th century when Italian miners faced the issue of water pumps not exceeding a height of 10.3 meters. Experiments by Gasparo Berti and Evangelista Torricelli led to the realization that air pressure influences water levels. Torricelli's mercury barometer demonstrated that atmospheric pressure affects altitude, revolutionizing scientific thought and paving the way for modern weather forecasting tools.

Takeaways

• 🌿 Aristotle believed that a vacuum couldn't exist, claiming that nature filled empty spaces with matter.
• 🧪 This idea was proven wrong, and vacuums became essential for instruments like the barometer, which measures air pressure.
• 🌪️ Barometers are critical for predicting weather events like hurricanes and tornadoes by detecting changes in air pressure.
• ⛏️ In the early 17th century, Italian miners found that their water pumps couldn't raise water higher than 10.3 meters, sparking interest in the nature of vacuums.
• 🔬 Galileo and others theorized that sucking air out created a vacuum, but there was still a limit to how high water could rise.
• 💧 Gasparo Berti's experiment with a water-filled tube successfully demonstrated the existence of a vacuum, but controversy persisted about the forces at play.
• 🌡️ Evangelista Torricelli shifted the focus, proposing that atmospheric pressure, not a vacuum's force, influenced the water levels in the tube.
• 📏 Torricelli used mercury instead of water, resulting in a much shorter column (76 cm), supporting his theory that air pressure dictated the height.
• 🏔️ Blaise Pascal confirmed Torricelli's theory by showing that the mercury level dropped as atmospheric pressure decreased with altitude.
• 🚫 Mercury barometers were commonly used until 2007, when restrictions on mercury's toxicity led to their discontinuation in Europe.

Q & A

What was Aristotle's belief about vacuums, and why was it significant?

Aristotle believed that a true vacuum could not exist because nature would immediately fill any empty space with surrounding matter. This idea was significant as it influenced scientific thought for nearly 2,000 years, making the concept of a vacuum controversial and largely unchallenged.

Why is a vacuum important in the function of a barometer?

A vacuum is crucial in a barometer because it allows the instrument to measure air pressure accurately. Atmospheric pressure influences the level of mercury (or other fluids) in the barometer, making it an essential tool for predicting weather patterns.

What problem did 17th-century Italian miners encounter, and how did it raise questions about vacuums?

Italian miners found that their pumps couldn't raise water higher than 10.3 meters. This limitation raised questions about whether a vacuum could exist, as scientists like Galileo speculated that air pressure and the vacuum created by the pump were influencing the height of the water.

How did Galileo explain the limitation of raising water to a height of 10.3 meters?

Galileo proposed that air was being sucked out of the pipe, creating a vacuum, and water rose to replace it. However, he believed this vacuum could only exert a limited force, which restricted the water to 10.3 meters.

What was the significance of Gasparo Berti’s experiment, and what did it demonstrate?

Gasparo Berti conducted an experiment where he created a stable vacuum by filling a tube with water and showing that a vacuum could exist at the top of the tube after the water level dropped to 10.3 meters. This demonstrated the possibility of creating a vacuum, challenging Aristotle's long-held belief.

How did Evangelista Torricelli approach the problem differently from Galileo?

Torricelli focused on the role of atmospheric pressure instead of the vacuum. He hypothesized that the atmospheric pressure outside the tube was responsible for holding the water (or mercury) in place, balancing the pressure inside the tube.

Why did Torricelli use mercury in his experiment instead of water?

Torricelli used mercury because it is denser than water, which allowed him to create a more compact barometer. The mercury column stood only 76 centimeters high, making the instrument easier to handle while still demonstrating the effects of atmospheric pressure.

What evidence ultimately supported Torricelli's theory of atmospheric pressure?

Blaise Pascal's experiment provided strong evidence for Torricelli's theory. He took a mercury barometer up a mountain and demonstrated that the mercury level dropped as atmospheric pressure decreased with altitude, confirming that air pressure affected the mercury's height.

Why are mercury barometers no longer widely used today?

Mercury barometers were phased out after 2007 due to concerns about mercury's toxicity. Regulations in Europe banned their production, leading to the development of alternative instruments to measure atmospheric pressure.

How did Torricelli's work challenge the traditional views of his time?

Torricelli's work challenged the long-held belief, based on Aristotle’s theories, that air has no weight and exerts no pressure. His experiments demonstrated that atmospheric pressure was a real and measurable force, changing the way scientists understood the properties of air and vacuums.