One of standard measurements that we take for granted these days is the charge of a single electron. This is a vivid example of how scientific knowledge has exploded during the past century. In 1870, there was no concept of an electron, and atoms were just very crudely becoming accepted.
After the turn of the previous century, it was generally accepted that there were atoms, and that electrons were likely a part of them, but no one knew much about them. We still have not all of the answers, but Robert Milliken elucidated the intrinsic charge of the electron in xxxx.