So hm ... the 1881 census shows a Reuben Isaacs born c1872 in Aldgate, Middlesex, eldest child of parents Woolf, c1850 Aldgate, and Priscilla, c1850 Spitalfields, in St Bodolph Aldgate.
They married in 1871 in London City registration district:
http://freebmd.rootsweb.com/cgi/search.pland she was Priscilla Lyons.
But in 1851, Woolf Isaacs, born 1847 Aldgate, is the son of Benjamin and Esther. Two people have been correcting Woolf's name at Ancestry, btw, one very recently: from Hoolf to Woolf and then Wolf. They don't state their connection, if any. In 1871, that Woolf is with brother Lewis and sister Elizabeth. Since the marriage was in the same registration district, in the September quarter, i.e. after the census, this could be the right Woolf Isaacs, or not.
There are other Woolfs born either side of 1850, but none has a father Samuel in censuses.
Oh, interesting, though. Reuben may have been enumerated twice in 1881 ... or there are two identical Reubens. Reuben Isaacs, c1872 Aldgate, is with grandmother Jane Isaacs in St Bodolph Aldgate. ... And in fact there were! September quarter and December quarter 1872, in London City registration districts, two Reuben Isaacs-s (not to mention one in the same reg dist in 1873). Well, we seem to have the right Reuben with father Woolf, anyway. I was just hoping that Jane would be Woolf's mother, but no such luck.
Reuben must have been the one who emigrated to Australia, if his son was a young boy there at the time of the gift? Is it possible he went to SA first? FindMyPast
http://www.findmypast.co.uk/passengerListPersonSearchStart.actiondoesn't show an R Isaacs travelling to Australia at the right time, but there are voyages by R Isaacs, male with unstated dob, travelling to Durban in 1902 and 1904. But there is also an R born c1872 travelling to Melbourne in 1932 -- several years after the book gift in Australia. A visit home?
David Harris was born in the City of London in 1852:
http://angloboerwar.com/forum/7-genealogy-and-family-research/5314-col-sir-david-harris-1852-1942Same time and place as Reuben's father Woolf Isaacs.
David Harris's parents were Woolf Harris and Phoebe Romaine, married 1848 City of London:
(and I swear this community was as bad as my stupid Hill clan in Cornwall/Devon with their Jameses and Williams)
http://www.geni.com/people/David-Harris/6000000012646217984and of course Barney Barnato/Isaacs was born 1852 Whitechapel. And his mother was Leah Harris 1816.
The 1851-61-71 censuses have Woolf Harris born 1827-29, Aldgate, Houndsditch, Whitechapel.
In 1841 in St Bodolph Aldgate, his parents Solomon and Susan are old enough (50+, 55+) to have a child born c1816, just in case maybe David Harris's father and Barney Barnato's mother were siblings. Oh duh, they were, as the link I posted way back, in this thread, shows:
http://www.geni.com/people/Leah-Isaacs/6000000003071284013Leah Harris's father was Solomon, a general dealer, per her marriage certificate.
Woolf Harris's father was Solomon, a dealer, per the 1841 census.
Not that there couldn't have been two of
them.
That connects Col. Sir David Harris and Barney Barnato, assuming one Solomon Harris.
David's father Woolf Harris was the brother of Barney's mother Leah Harris Isaacs.
Now, do Marianne's Isaacs in-laws connect up with Barney Barnato's Isaacs-s, and thus with David Harris?? Or connect with them another way? Or not at all ...?

There's a start, anyway!
Solomon Harris and Susan had children:
- Leah Harris who married Isaac Isaacs and had son Barney Barnato
- Woolf Harris who married Phoebe Romaine and had son David Harris
David Harris and Barney Barnato were first cousins.
... Of course, now we google the names together and see that David Harris was Barney Barnato's nephew:
http://www.sahistory.org.za/dated-event/col-david-harris-nephew-barney-barnato-partner-cecil-john-rhodes-and-cape-parliamentariabut I don't thiiiink so.
Right, other sources say cousin. I should've just googled first.
