> Maybe rubber turtles with ballast to keep them just below the surface would work better.
> Howard

I think I remember a TV show about using bottles with paper in them to find out about ocean currents. When someone on a ship spotted a bottle, they would pull it up and mark down the date and coordinates on the paper inside, then toss it back in. Eventually it would wash up somewhere and someone could plot out the current it followed.

I think this was when big sailing-ships were in heavy use, though I don't remember a date.

NormalAsylum