If anyone claims “The horizon always rises to eye level” but hasn’t tested it, they are being dishonest.

The Claim

The claim that the horizon always rises to eye level is very common and quite old. One early claims are from Samuel Rowbotham in his book “Earth not a Globe” from 1881. From page 172: “…it is shown that the surface of the sea appears to rise up to the level or altitude of the eye…” This is also the topic of his experiment 15 in the book. Sadly this experiment is horribly conceived and falls far short of an actual scientific experiment.

Rowbotham used an unspecified instrument called a “Clinometer”. He does not describe this device. Even in 1881, there were instruments to accurately measure vertical angles called Theodolites. As we don’t know what this “Clinometer” is, the exercise is not repeatable, thus not an experiment. Rowbotham observed the horizon from two locations in a hotel but failed to state the elevation above sea level. Fortunately, this old hotel still stands. The height has been calculated to be no more than 150 feet above sea level.

Rowbotham makes a curious statement about the expected angular dip. He says he expects a “considerable angle downwards”. This is not predicted by the globe model. Instead, at 150 feet, the expected dip is very slight. The maximum globe earth, non refracted, predicted angular dip for this height is 0.217 degrees. It is unclear if the clinometer Rowbotham used had a resolution this accurate. It is also unclear if Rowbotham calculated the expected dip, as would be expected in a rigorous experiment.

As cameras were not as commonplace at the time, we cannot expect photographic evidence. However, third party attestation would be helpful, this is not provided either. Experiment #15 does not provide details about the weather conditions such as wind, temperature, or cloud cover. Neither does he include the time of day or tide position.

This is typical of the sloppy, unscientific content in the rest of the book. I’ve read the entire book. I’ve gone over the “experiments” several times. It is all quite poor quality.

Test it

Today it is very easy to test this yourself.

At the hardware store buy two feet of 1inch inner diameter clear vinyl pipe and two 90 degree elbows. Total cost under $10. Put water and food coloring in it, I used blue windshield wiper fluid. Cut the tube in 3 pieces and piece together into a U shape, fill with water partway up both ends.

Go to the highest place you can find like a good-sized hill or top of a building. It’s good to do it near the ocean but this is not necessary, a really high place will do, it must be significantly higher than any place you will be viewing in the test. Look towards the lowest area you can see. Unless you are near Death Valley or similar, it will be above sea level, so will give an advantage to the rising to eye level claim. Line up the top of the water in the two vertical pipes and sight along them.

If you would like, I will post anyone’s findings here. Take at least three pictures sighting along the tops of the two water lines. The three pictures are where the line is in the middle of the frame, in the bottom of the frame and the top of the frame. Why? Ignorant flat earthers actually count pixels and if the leveled water isn’t exactly centered they make the unfounded claim that if the photo isn’t centered it’s skewed. So, taking three photos like this will prove this claim is untrue.

Historically documented

The fact that the horizon drops with elevation has been well known for centuries. Al-Biruni used the horizon drop to calculate the radius of the earth.
The navigation manuals published by England for centuries lists the dip of the horizon at different elevations.