Mary, I am another one in Australia who is researching Moffats from Cornwall. My husband is descended from Josias Sleeman Moffatt, eldest son of Richard Moffatt, who married Mary Sleeman in 1796. Josias was born in 1798, and it was hids son, another Josias Sleeman Moffatt who emigrated to Australia in 1857. He is my husband's great-grandfather, was born in St Columb Minor in 1835 and sied in 1908.
I have been corresponding with Kathy via e-mail, and the letter she mentions was written to 'our' Josias by yet another Josias Sleeman Moffat, who was a clerk in the US Treasury when he wrote. He mentioned a brother Arthur, who, he said, was not yet married, and "has been in the wars, but is soon out of them".
I spent a week in the County Record Office in Truro a few years ago, and found a lot of fascinating details, including wills. I would be happy to exchange information with you, and look forward to hearing from you. Best wishes Eunice Fletcher