In Orthograffiti (WW78217), Richard Lederer showed that a single sound can be demonstrated by many letters. The sounds which concern us here are the long vowels, specifically the sounds of the 5 major vowels A, E, I, O, and U as they are pronounced in the reading of the alphabet. The sound symbols are those of the Phonetics List of the Oxford English Dictionary, Second Edition. However, I include a further parameter. The long vowel sound must either be preceded, or succeeded, by the short 's' sound.
"Sacred Manuscripts Boast Secret Ciphers,"
Word Ways: Vol. 40
, Article 23.
Available at: http://digitalcommons.butler.edu/wordways/vol40/iss4/23