I was always under the impression that the circular saw blade was due to a junior stone carver a short while after the wheel was invented. This particular stone carver had a part time job in an early stone wheel dealer's shop. It came about that on muddy paths, or roads such as they were, the conveyances with stone wheels had a terrible time on hills particularly after the rains, sometimes making it impossible to get any traction. He got the idea to carve a wheel with notches in it. Better to dig in when power was applied. He made them much thinner in order to facilitate seasonal change-overs and make his job a little less back-breaking. He was a clever junior, knowing there would be many repeat sales from those who cornered too quickly and had the wheel snap in two from the stresses put upon them. He had a lucrative set-up but, as always, as centuries went by, the wheel evolved to eventually being made of wood, then steel. This was a great advancement. Now coming forward to Sister Tabitha, a very clever lady. She watched the early road builders building those corduroy roads and the tough job of having to lay the logs and cut the ends cleanly in order to install the guard rails according to code. She got the idea of putting a steel disc with sharpened edges on one of the wagons axles. Trial and error followed for a time until eventually, with modified gearing, she won the day. Evolution as usual brings us to what we have today. Just a look at a bit of history.