Several years ago, I remember reading about an experiment, and I thought it was in Newton's Principia, so the experiment was conducted in that time frame. The experiment involved timing the fall of a glass ball from a great height indoors (like the inside of a cathedral). Timing was done by watching a pendulum. There were several observers for each experiment, each one reporting their answer independently and then the final answer was obtained by taking the mean of each individual timing.
The thing that caught my eye is that the times were reported in seconds and thirds (1 third=1/60 second). That was the first time I had ever heard of a second as being the second division of an hour, (the first being minutes), and there being further divisions by 60 each time.
I have skimmed a paper copy of Principia in my school library and didn't find that experiment. I'm pretty sure I didn't imagine the experiment (I wouldn't have come up with thirds) but I can't find a reference to it. I want something to point to when I point out that a "third" is a real unit of time.
Can anyone help me find that experiment?