Darn, the sharpshooting canine is right, it wasn't the G string they added as the fourth string, I posed the question wrong!
Ralphe Armstrong, the man who played with Mahavishnu and Jean-Luc Ponty and is now a college professor for music history, says in a current interview in a German bass mag that the fourth string was added in Germany in 1779, the "invention" then conquering Europe quickly with one exception: The Brits - as with the EURO or right lane driving, really ANYTHING sensible for that matter - held out with formal adoption until 1846! He also mentions that the bass tuner was a German invention - in 1778 by a chap called Ludwig Bachmann at the behest of the King of Prussia (who perhaps preferred his music in tune?).
And he confirms that he had an endorsement deal with Gibon for his fretless RDs and Victories and that it all went foul when Gibson fired its whole artist relations dept so that he would have had to negotiate a new deal which he didn't feel like doing. He plays Dean these days, the Edge SQ-5 and -6 models mostly. There are acouple of pics of him in the interview playing his fretless Victory Artist with sax legend Eddie Harris as late as 1986.
Trust Gibson to have someone with jazz rock credibility playing their outlandish basses and then mess it up!