View full lesson: http://ed.ted.com/lessons/the-history-of-the-barometer-and-how-it-works-asaf-bar-yosef

A barometer is an instrument that measures air pressure, allowing weather forecasters and scientists to better predict extreme weather events. Despite its incredible usefulness, inventing the barometer was no walk in the park. Asaf Bar-Yosef describes the series of scientists and events that contributed to the birth of the barometer -- and explains how it actually works.

Lesson by Asaf Bar-Yosef, animation by Reflective Films.