Aristotle once claimed that “Nature fears empty space,” suggesting that a true vacuum, or a space with no matter, couldn’t exist because surrounding matter would rush in to fill it. However, this idea was eventually proven wrong. A vacuum is actually a crucial part of the barometer, a tool used to measure air pressure. Air pressure is important because it relates to temperature and can indicate extreme weather events like hurricanes and tornadoes. This makes barometers essential for weather forecasters and scientists.
Understanding how a barometer works and its invention took a long time. For nearly 2,000 years, Aristotle’s theory about the impossibility of a vacuum seemed true in everyday life. Few questioned it until a practical need arose. In the early 17th century, Italian miners faced a problem: their pumps couldn’t lift water higher than 10.3 meters. Some scientists, including Galileo Galilei, suggested that removing air from the pipe allowed water to rise, but only up to 10.3 meters. The idea of a vacuum was still controversial.
Galileo’s theory sparked interest, leading Gasparo Berti to conduct a clever experiment. He filled a long tube with water, placed it in a shallow pool with both ends sealed, and then opened the bottom end. Water poured out until the level in the tube was 10.3 meters, leaving a gap at the top. No air entered the tube, creating a stable vacuum.
Despite Berti’s demonstration, not everyone accepted Galileo’s idea of a mysterious force in the vacuum. Evangelista Torricelli, a student and friend of Galileo, approached the problem differently. He considered that the surrounding air pressure might be the only factor keeping the water level from dropping further. The water level would decrease until the pressures were equal, which happened at 10.3 meters.
Galileo and others believed that atmospheric air had no weight and exerted no pressure. Torricelli decided to repeat Berti’s experiment using mercury instead of water. Mercury is denser, so it fell farther, resulting in a mercury column of about 76 centimeters. This created a more compact instrument and supported Torricelli’s idea that air pressure was the key factor.
A variation of the experiment used two tubes, one with a large bubble at the top. If Galileo’s interpretation had been correct, the larger vacuum should have lifted the mercury higher. However, the levels in both tubes were the same. Blaise Pascal further supported Torricelli’s theory by taking a mercury tube up a mountain, showing that the mercury level dropped as atmospheric pressure decreased with altitude.
Mercury barometers based on Torricelli’s model were widely used to measure atmospheric pressure until 2007, when mercury’s toxicity led to their discontinuation in Europe. Torricelli’s invention, born from questioning long-held beliefs about vacuums and air pressure, demonstrates the power of thinking outside the box—or the tube—to make significant scientific advancements.
Gather materials to simulate Torricelli’s mercury experiment using water and a clear tube. Observe how the water level stabilizes and discuss how this demonstrates air pressure. Reflect on how this experiment challenged Aristotle’s vacuum theory.
Divide into two groups and prepare arguments for a debate: one supporting Aristotle’s vacuum theory and the other supporting Torricelli’s findings. Use historical context and scientific reasoning to defend your position.
Research how modern barometers are used in weather forecasting. Create a presentation explaining how changes in air pressure can predict weather events. Discuss the impact of Torricelli’s invention on today’s meteorology.
Conduct an experiment to measure atmospheric pressure at different altitudes. Use a portable barometer or a smartphone app to record pressure changes. Analyze the data and relate it to Torricelli’s mountain experiment with Pascal.
Develop a timeline that traces the history of the barometer from Aristotle’s era to the present day. Include key experiments and figures like Berti, Torricelli, and Pascal. Highlight how scientific understanding evolved over time.
Aristotle famously claimed that “Nature fears empty space,” suggesting that a true vacuum, or a space devoid of matter, could not exist because surrounding matter would immediately fill it. Fortunately, he was proven wrong. A vacuum is a key component of the barometer, an instrument used to measure air pressure. Since air pressure correlates with temperature and rapid shifts in it can contribute to hurricanes, tornadoes, and other extreme weather events, a barometer is essential for weather forecasters and scientists alike.
How does a barometer work, and how was it invented? It took a long time for this understanding to develop. For nearly 2,000 years, the theory of Aristotle and other ancient philosophers regarding the impossibility of a vacuum seemed to hold true in everyday life, and few questioned it until necessity arose. In the early 17th century, Italian miners faced a significant problem when they discovered that their pumps could not raise water more than 10.3 meters high. Some scientists, including Galileo Galilei, proposed that removing air from the pipe allowed water to rise and that this force was limited to 10.3 meters. However, the existence of a vacuum was still considered controversial.
The excitement surrounding Galileo’s theory led Gasparo Berti to conduct a simple yet brilliant experiment to demonstrate the possibility of a vacuum. He filled a long tube with water, placed it in a shallow pool with both ends plugged, and then opened the bottom end, allowing water to pour out until the level in the tube reached 10.3 meters. With a gap remaining at the top and no air entering the tube, Berti successfully created a stable vacuum.
Despite this demonstration, not everyone accepted Galileo’s idea that this empty void exerted a mysterious yet finite force on the water. Evangelista Torricelli, Galileo’s young pupil and friend, approached the problem differently. Instead of focusing on the empty space inside the tube, he considered what else could be influencing the water. He realized that the pressure from the surrounding air could be the only factor preventing the water level in the tube from dropping further. The water level decreases until the pressures are equal, which occurs at 10.3 meters.
This idea faced resistance, as Galileo and others had traditionally believed that atmospheric air had no weight and exerted no pressure. Torricelli decided to repeat Berti’s experiment using mercury instead of water. Because mercury is denser, it fell farther than water, resulting in a mercury column of about 76 centimeters. This allowed Torricelli to create a more compact instrument and supported his idea that weight was the deciding factor.
A variation of the experiment involved two tubes, one with a large bubble at the top. If Galileo’s interpretation had been correct, the larger vacuum in the second tube should have exerted more suction and lifted the mercury higher. However, the levels in both tubes remained the same. The ultimate support for Torricelli’s theory came from Blaise Pascal, who took a mercury tube up a mountain and demonstrated that the mercury level dropped as atmospheric pressure decreased with altitude.
Mercury barometers based on Torricelli’s original model remained one of the most common ways to measure atmospheric pressure until 2007, when restrictions on the use of mercury due to its toxicity led to their discontinuation in Europe. Nevertheless, Torricelli’s invention, born from a willingness to question long-accepted beliefs about vacuums and the weight of air, exemplifies how thinking outside the box—or the tube—can have a significant impact.
Barometer – An instrument used to measure atmospheric pressure. – Example sentence: The meteorologist used a barometer to predict the approaching storm by observing changes in atmospheric pressure.
Vacuum – A space entirely devoid of matter, including air. – Example sentence: In a vacuum, sound cannot travel because there are no air molecules to carry the sound waves.
Pressure – The force exerted per unit area on the surface of an object. – Example sentence: The pressure inside a closed container increases when the temperature rises, according to the ideal gas law.
Mercury – A dense, silvery metal that is liquid at room temperature, often used in thermometers and barometers. – Example sentence: The mercury level in the barometer dropped, indicating a decrease in atmospheric pressure.
Experiment – A scientific procedure undertaken to test a hypothesis by collecting data under controlled conditions. – Example sentence: The physics students conducted an experiment to measure the acceleration due to gravity using a pendulum.
Air – The invisible gaseous substance surrounding the Earth, a mixture primarily of oxygen and nitrogen. – Example sentence: The composition of air can affect how sound waves travel through the atmosphere.
Temperature – A measure of the average kinetic energy of the particles in a substance, indicating how hot or cold it is. – Example sentence: As the temperature of a gas increases, the speed of its molecules also increases, leading to higher pressure if the volume is constant.
Weather – The state of the atmosphere at a particular place and time, including factors such as temperature, humidity, and precipitation. – Example sentence: Scientists study weather patterns to understand climate change and predict future atmospheric conditions.
Altitude – The height of an object or point in relation to sea level or ground level. – Example sentence: As altitude increases, atmospheric pressure decreases, which can affect the boiling point of water.
Density – The mass per unit volume of a substance, often expressed in kilograms per cubic meter. – Example sentence: The density of a material determines whether it will float or sink when placed in a fluid.
