Atmospheric pressure Perspective Perfectly good logic Commentary

Evangelista Torricelli, Blaise Pascal atmospheric sciences

Atmospheric pressure

• Evangelista Torricelli, a student of Galileo,
• invented the mercury barometer,
• but its use created a mystery
• that scientists before Pascal could not explain.
• Torricelli showed that if you take a glass tube closed on one end,
• fill it with mercury, and invert it into a cistern,
• not all of the mercury leaves the tube,
• leaving a gap at the closed end.
• Water barometers had been made before
• but no one before Torricelli realized
• that the weight of the atmosphere
• balanced the weight of the liquid in the tube.
• The difficulty was that scientists believed
• that air was weightless
• and that a vacuum was an impossibility.
• After all, if nothing was in the gap then what propagated the light?
• Pascal showed that the gap was a vacuum,
• that the mechanical weight of the atmosphere
• decreased as you ascended. If you hike high enough,
• you would reach the vacuum of space.

Perspective

• From an airplane window
• Canada looks flat. Mountains and valleys
• are smashed into a plain of snow.

Perfectly good logic

• Perfectly good logic
• can begin with
• foregone conclusions.
• Perfectly good logic
• convinced everyone
• light couldn’t pass
• through a vacuum.
• But that was when
• outer space was filled
• with luminiferous aether
• and air with phlogiston.