Magick Without Tears by Aleister Crowley
Added for references to Theta, Θ.
Chapter XXXIX: Prophecy
7: This Sun & Moon symbolism flows from Crowley’s work with Greek, Tarot and Hebrew. “Set” as Sigma-Theta or as Shin-Teth. Taking the numbers for the corresponding Tarot Trumps from the Thoth Deck, we get XX + XI = 31. See O.T.O. Newsletter, No. 7-8, p. 9 ff, “Liber MCCLXIV The Greek Qabalah” and No. 9, p. 31 – WEH.
See also Liber V vel Reguli. To clarify: the Greek letter Sigma Σ can also be written as C, which approximates the symbol for the moon; a capital Theta, Θ, approximates the symbol for the Sun. Shin-Teth are the Hebrew equivalents. I am not quite clear on how Crowley reads 3.141593 from ShT + ALHIM: reducing each letter to units gives the sequence 3, 9, 1, 3, 5, 1, 4 and there is no way one can get the required order from that with a constant step. To get 3.1415 from ALHIM is not a simple reversal of the order but requires writing the numbers around an Invoking Pentagram and reading them in the order of the corresponding Banishing Pentagram. See A Note on Genesis – T.S.
See also: Hubbard’s definitions for Theta, etc.