Magick Without Tears by Aleister Crowley

Source: http://hermetic.com/crowley/magick-without-tears/mwt_39.html

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.