While it's true that unipolar magnets can't exist, this isn't a problem for the Flat Earth. This is because ring magnets, which are shaped like (you guessed it!) a flat disk, are capable of having radial magnetization. In a radial magnet, one magnetic pole is at the center and other is at all points on the edge of the magnet. A magnet like this can be found in loudspeakers, and perfectly replicates what is found on the Earth.
As mariners take to sea with them charts constructed as though the sea were a level surface, however these charts may err as to the true form of this level surface taken as a whole, it is clear, as they find them answer their purpose tolerably well - and only tolerably for many ships are wrecked owing to the error of which we speak - that the surface of the sea is as it is taken to be, whether the captain of the ship "supposes" the Earth to be a globe or anything else. Thus, then, we draw, from the common system of "plane sailing," a practical proof that Earth is not a globe.
133) In direct sunlight a thermometer will read higher than another thermometer placed in the shade, but in full, direct moonlight a thermometer will read lower than another placed in the shade. If the Sun’s light is collected in a large lens and thrown to a focus point it can create significant heat, while the Moon’s light collected similarly creates no heat. In the "Lancet Medical Journal,” from March 14th, 1856, particulars are given of several experiments which proved the Moon's rays when concentrated can actually reduce the temperature upon a thermometer more than eight degrees. So sunlight and moonlight clearly have altogether different properties.
Astronomers tell us that, in consequence of the Earth's "rotundity," the perpendicular walls of buildings are, nowhere, parallel, and that even the walls of houses on opposite sides of a street are not! But, since all observation fails to find any evidence of this want of parallelism which theory demands, the idea must be renounced as being absurd and in opposition to all well-known facts. This is a proof that the Earth is not a globe.