Before Galileo, the scholars believed that the bigger object could reach the ground faster than the smaller one,... -- the's are not needed?
However, Galileo climbed to the top of the Leaning Tower of Pisa, letting two rocks with different volumes drop to the ground at the same time, therefore proving to his friends whom he had brought to watch the experiment that Aristotle was wrong. -- would it be better to put the more important statement (let drop...prove...) in the main clause instead?