Comment by throwway120385 3 days ago
That's an interesting way to measure the passage of time -- just use something that produces a "regular distance" and derive a way from kinematics to calculate the acceleration from the change in the distance.
Well the other problem is knowing where you are. The sun/stars can give you latitude. Longitude was nearly impossible until the advent of the marine chronometer in the latter part of the 18th century, and not "standard" on ships until the mid-1800s. There were earlier versions, which had poor accuracy and were not much better than dead reckoning
> You drop one end of the rope in the water, and count how many knots pass you in a given time.
Given that you're dragging the rope behind you, won't this number be zero?
The way boats historically measured speed was by dragging a rope behind them. The rope has knots tied with exact spacing. You drop one end of the rope in the water, and count how many knots pass you in a given time. That's then your speed in knots.