Originally Posted by kerry

I think it has less to do with time and place and more to do with a sharp person who understood differntials and knew how to communicate that knowledge effectively in a very simple manner. I think that a pretty high percentage of people who knew exactly how and why differentials worked couldn't have come up with that simple model to explain it to the ignorant.
I've looked at a number of differentials in my day, saw what was happening but didn't understand it.