Blaise Pascal (1623 – 1662)
Instrument to measure weight of air height of mountains.
NARRATOR: Until now, we focused on the work done in Italy during the early and mid-17th centuries. However, by then, French scientists were also very active. And it was the French infant prodigy, Mr. Blaise Pascal, who finally proved, that air has weight. Mostly we know Mr. Pascal for his work on pressure. But you will be surprised that this engagement with the work on “air” finally led him to his work on pressure. To learn more about how he proved that air has weight, let’s invite Mr. Pascal himself! Welcome, Sir! How are you?
PASCAL: Thanks, I am fine. What about you?
NARRATOR: Great! It is a pleasure to be with you. So, can you tell us how it all got started?
PASCAL: Sure! Well, I heard about the debate about the vacuum. And one particular event in this debate that excited me the most was the experiment done by Torricelli.
NARRATOR: Why?
PASCAL: Because it suggested that the atmosphere was like an ocean of water above our heads, pushing down against the surface, indicating that air has weight. The best part was how Torricelli interpreted it from the changing level of mercury in the tube.
NARRATOR: Hmm… But how did you get to know about this experiment?
PASCAL: I learned of it from M. Petit, superintendent of fortification.
Narrator: But what was your thought on this?
PASCAL: I wondered if Torricelli was right. So along with Petit, I decided to repeat his experiment. Further, I also devised an experiment to test the Aristotelian thought about the vapors of the liquid filling the space in a barometer.
NARRATOR: Vapors?
PASCAL: Yeah, it was a concern to be addressed.
NARRATOR: Why?
PASCAL: Aristotelians argued that variation in the level was because of vapors of the liquid present in the tube rather than the surrounding air.
NARRATOR: And you wanted to settle this?
PASCAL: Yes.
NARRATOR: So what was your idea?
PASCAL: Well, I devised an experiment where I compared the levels of wine to water in the tube. The idea was that since wine was more spiritous than water, it should stand lower if the Aristotelians were correct. (more vapors would mean more pushing against the liquid column).
NARRATOR: And were they correct?
PASCAL: I performed it publicly, inviting the Aristotelians to predict the outcome. But they were all proved wrong.
NARRATOR: But this doesn’t prove that Torricelli was right either.
PASCAL: Really! I don’t think so. Since wine weighs less than water, it is pushed in further by the same amount of force from the air. So it should be the force of external air pushing on the basin that causes the liquid to stop falling.
However, I went even further to test this mechanical theory. The idea was that if, as suspected, the air had lateral weight, the weight of the air should be less in higher altitudes. So I thought that climbing a gigantic mountain would reduce the amount of air in the sky, reduce the weight of the air, and lower the level of mercury in the barometer.
NARRATOR: So did you take it to the top of a mountain?
PASCAL: No, I did not. I had a lot of health issues. So I convinced my brother-in-law Florin Périer to hike to the top of the volcano, Puy de Dôme, and along the way, measure the height of the mercury in the tube of a barometer. In September 1648, he made the hike to the summit and recorded the levels of mercury. On September 22, he wrote me a letter with the results, which proved that Torricelli was right. The atmosphere has a weight that presses down on the surface of the Earth.
Soon this apparatus became a new scientific tool to measure atmospheric pressure and the height of mountains.
NARRATOR: Wow! And what about the vacuum?
PASCAL: What about it?
NARRATOR: Did you believe in its existence?
PASCAL: Yes.
NARRATOR: But what made you believe that it can exist?
PASCAL: Well, it was because there were a lot of contradictions, like if nature abhors a vacuum, then why does it allow it!
NARRATOR: Yeah, you are right. It sounds logical.
PASCAL: You know it was during this time that I developed the modern scientific idea of pressure, physical forces exerting against substances.(pressure=force/area)
NARRATOR: Great! Thank you for sharing this with us! Even I did some research and found that in 1647 René Descartes attached a graduated scale to the tube to record any changes attributable to the weather. While in 1660, Robert Boyle named it a Barometer which means an instrument for measuring weight. A term that got soon adopted in the Latin, French, German, and Italian languages.