This is O' Nolan's book, which sums up all his earlier publications on the subject. I have faithfully re-typeset the book from my fair copy, and with feedback, and help from too many to count, I have made minor adjustments, as listed on the front fly. Again, my effort has been to reflect as far as possible the original layout, and to support the usage of seanchló, though the newer font is here favoured because the archaic fonts with long 's' and long 'r' are easily confused with each other, and also with 'f'. The newer font avoids this fault, which brought seanchló into disregard.