Yes, it is possible. Rowbotham's experiments do not discount the possibility of concavity, only convexity. It's called "Earth Not a Globe" not "The Earth is Flat". It is primarily a book of skepticism against the globe model, and an exposé that what know about astronomy and the earth is wrong.
There are societies who believe that the earth is concave and who will often quote Rowbotham's works as a disproof of the globular model. It was Rowbotham's post-enlightenment questioning of the globe, in fact, which got people thinking about other models. Per the concave earth theory; there are some models which propose that we live on the inside of a bowl, and there are others which propose that we live on the inside of a hollow earth. Look up the book "The Cellular Cosmogony" by Cyrus Teed.