Dr Rowbotham made proper experiments and observations to come to the conclusion the earth is flat, instead of pure speculation like you are suggesting.
The book may have been written in the 1800s, but it has yet to be proved incorrect, despite round earthers desperately trying to prove otherwise.
If he did, then why the whole scientific disciplines can't work with Flat assumption?
Why all those fenomena show behavior adequate for Globe model?
If his book is "yet to be proved incorrect", why are his "conclusions" useless?
Why even "plane sailing" helps only on short distances, within, say, Red, Black, or Yellow sea, and on ocean would make you go in completely wrong direction?
Why so many Flat Earthers have to deny so many things, like gravity, satellite technology, ISS, Moon landing, Mars rovers, interplanetary probes...?