two new sources checking in on JACK

[Laurence Horn]

The often entertaining, if not always reliable, Brewer's Dictionary
of Phrase and Fable (up to the reader to guess which is which), first
published in 1870 and periodically revised since (I'm using the Ivor
Evans edition of 1970), takes most of the JACKs to 'impl[y] smallness
or inferiority of some kind', ranging from our old farthing to
various flags, drinking vessels, bowling devices, pieces of leather
clothing, and counters for gambling.   Brewer doesn't list "jack
shit", but then he wouldn't; however, he also doesn't give "not worth
(a) jack" as a phrase, while he does elsewhere list 'not worth a
damn' (incidentally dismissing the derivation from the "dam" coin).

Alfred Holt's _Phrase Origins_ (1936) describes the "jack" of
'farthing' fame to mean more generally 'a small or counterfeit coin',
again something one would expect things not to be worth, but again
without the corroboration of a 'not worth jack' gloss or cite.

So these sources lend support to Jesse's observation of
discontinuity, despite the obviously compelling nature of my argument
that a word regularly referring to a small or worthless coin or
object OUGHT to show up in phrases of the form 'not worth (a) ____'.
Oh well.

larry