According to The Copper Family Song Book, which contains a few facsimiles of Brasser's handwriting, including the relevant one here, he wrote 'Here's a dew sweet lovely Nancy ten thousand times a dew', which I suspect was a spelling error resulting from unfamiliarity. He also wrote 'I am goeing round the ocan', and 'Come chaing your ring', though he got that one right the second time. In times past spelling was prone to error, particularly in less common words - much as it is now really.