Can you see the other side of the lake? I don't know if it will work if you can, you're suppose to compare against the horizon, the water only makes the horizon as smooth as possible.
You can't see the other side. It's a very big lake.
So this morning I walked to Lake Michigan. It's only about 15 minutes from my apartment, and it was a nice morning for a walk. Plus, one nice thing about being out at 6:30 in the morning is no homeless ask you for change.
When I got to the lake, I was disappointed that I couldn't take any pictures from the pedestrian bridge over the highway as I had hoped, as trees obstructed the view. So I had to settle for the shoreline. Fortunately the shore of Lake Michigan along most of Chicago is built up with rocks and concrete, so by standing on the large concrete blocks at the top of the rocky slope up from the lake, I could get the camera a good 20 feet above water level. I wish I could have gotten higher, but there was nowhere to stand to take a picture.
I tried taking some with a straight board I found, but I decided that I had no reason to believe any discrepency I found was due to the board and not the horizon, as the board seemed just as likely to be slightly curved as the horizon, if not more so, and I thought that taking photos and using the single row select tool would be a better judge of horizontal than a possibly warped board. I did notice that the horizon appeared to be slightly curved, but when I climbed down to the slope and held my head a mere 3 feet above the water level, it appeared equally curved, so I decided it was an illusion.
So here's the picture I took. The camera was zoomed out as much as possible, so as to capture the longest stretch of horizon that I could. (I actually took several, but I'm tossing the ones with the board, and this was the one where the camera was closest to level. They were all pretty much the same.) This is resized down to 800x600, but you can click on it for the full sized, unaltered version.
That horizon looks pretty damn level, wouldn't you say? Of course, I still think the Earth is round, but hopefully this will convince doubters that you can't use the "the horizon looks curved" argument to prove the Earth is round. Personally I found the equations more convincing than the photograph, but then I'm a mathematician.
Now I can honestly say that I've actually performed an experiment someone asked of me on the boards. How many of you can do the same?