Hi Jacqui
For the return journey to Ireland the only list I could find was see link
UK, Incoming Passenger Lists, 1878-1960
http://search.ancestry.com/search/db.aspx?dbid=1518 I could not find William Weir in the list, you may have better luck !
I also tried the - City of Berlin - N.Y. to Queenstown, Ireland but it only indicated voyages in 1887 and 1883 no voyages 1879-1882 N.Y. to Queenstown
Tim