Hello - I was just wondering if anyone had got any further with research of this man. I believe he died 3 October 1821 at Trincomalee, Ceylon (Sri Lanka). I think the 83rd were in Ceylon approximately 1817-27. Apparently there's an inscription to him at St Peter's Church, "Fort" (not sure where that is). The inscription is reproduced in a book of Ceylon Memorials by John Penry Lewis and gives a tiny bit more biography. It says he was 58 years old at death, which I have a problem with because it also says he married a daughter of Thomas Summerfield (1767-1833, also of the 83rd regiment). This would make William older than his father-in-law which seems a bit unlikely to me. I would think either William was perhaps 48 years old at death or alternatively married a sister of Thomas Summerfield, rather than a daughter.
If William's sister was Jean Geddes (the mother of Andrew Geddes Bain), she married in 1792 in Thurso.