André Ampère was born on January 22, 1775, in Lyon, France. He was the son of a well-to-do merchant. He mastered advanced mathematics on his own while still in his teens and learned Latin so he could read the works of the learned scientists.

Ampère was interested in a variety of subjects, including psychology, philosophy, astronomy, physics, and chemistry. He studied the nature of chlorine and iodine, but the credit went to Humphry Davy. Ampère analyzed Boyle's law and, in 1814, studied the molecular makeup of gases, independently coming up with what has become known as Avogadro's number. He spent most of his life teaching and giving lectures, primarily in mathematics and chemistry, at various institutions.

In 1819 a discovery occurred that had a profound effect on science in general, and Ampère in particular: Danish physicist Hans Christian Oersted placed a magnetized needle...