Lethbridge found his rates to be spiraling by what seems to me rather circuitous reasoning: following the leading fact that out-of-body experiences often include the viewing of the recently vacated physical body from a specific altitude and azimuth he connected the two points over 6-1/2 feet distant, the viewer and her body, with a spiral because of his finding that his pendulum rates tended to recur with a period of 20 inches and that the recurrence was not perfect, but rather suggested a relation analogous to that between the physical and astral planes. So a three dimensional Archimedean spiral, but what ought it's height function be? the only illustration I've found in Power of the Pendulum leaves quite a bit to the imagination! I haven't yet studied his data on false positions; perhaps those will delineate things for me a bit more sharply.
All this, not just to poke at Lethbridge, but to wonder out loud if Greeno could have followed the same trail independently, or perhaps come to the same end by another route