I don't know the origins, but it is an alternate idea than the one that Rowbotham put forward regarding the optical illusion of 'squishing/sinking' over the horizon of objects and the setting sun/moon/stars.
Basically, instead of this being a trick of perspective for otherwise straight light, the idea came about that the light curves at a gradual upward skewed (angled) parabolic arc, and it is this phenomena that explains this off in the distance 'sinking effect' at the horizon. It also explains why, after you see something 'set' behind the horizon, if you quickly climb vertically up, you can restore the image to view.
Now, given (assuming) a flat earth, there must therefore be some acceleration force that bends electromagnetic rays in an upwardly direction, this is the basis of Electromagnetic Acceleration Theory (EAT)