I'm afraid that I am also struggling to find anything on Isaac!!!
I note from an entry on the World Connect site, that Harriet and John had a daughter Hannah CHILMAN born in 1847.
http://worldconnect.genealogy.rootsweb.com/Database;
http://wc.rootsweb.com/cgi-bin/igm.cgi?db=wjansThis is curious, because although I cannot seem to find either Harriet and John on the 61 census as a couple (though there is a John who would fit with a different wife), I did find a Hannah of the right age, living with her grandfather Isaac
SMITH, who was a retired
Inland Revenue worker. Very curious!
RG9/297 Folio 132a
10 Cleveland Gr
StepneySMITH Isaac, Head, Married, 64, Superannuated Inland Revenue, b Matlock, Derbyshire
SMITH Hannah, Wife, 60, b Ripley, Derbyshire
CHILMAN Hannah, Grandaughter, 13, Scholar, b Homerton, Middlesex
This is quite a co-incidence don't you think? Why is it that you think that Isaac ARGYLE was born in Middlesex around 1800? Is it because this is what the World Connect contributor has posted perhaps?
Rick
