These are folk song arrangements that occupy a rather unusual place in Beethoven's oeuvre, much the way the transcription did in the work of the ever-busy Franz Liszt. Edinburgh-based publisher George Thomson developed a relationship with Beethoven in the early nineteenth century, engaging his services to arrange Scottish, Irish and Welsh folk songs. Their association would yield one hundred thirty-two such works in all, counting three English and two Italian folk song arrangements.
In this WoO 158b (or, as it is often given, WoO 158/2) British collection, Beethoven supplied the accompaniment to the songs, the instrumentation consisting of piano, violin and cello. The title, ethnic character and probable date of composition of the songs is as follows: 1) "Adieu my Lov'd Harp"; Irish; 1813; 2) "Castle O'Neill"; Irish; 1813; 3) "O Was not I a Weary Wight"; Scottish; 1817; 4) "Red Gleams the Sun"; Scottish; 1817; 5) "Erin! oh Erin!"; Irish/Scottish; 1815; 6) "O Mary ye's be Clad in Silk"; Scottish; 1815; 7) "Lament for Owen Roe O'Neill"; Irish; 1810.
To those interested in the folk music of Great Britain and to every note that Beethoven wrote, these are important efforts. To the average listener, however, these arrangements hardly divulge anything of significance about Beethoven's compositional talents. True, they show that he could adapt his skills effectively to the idioms of the various folk songs he arranged, to their ethnic flavors, to their individual modes of expression. Yet, the genre, of its very nature, could not allow him the freedom of expression to make these efforts his own creations. Still, in the study of this, one of the great masters of composition from any period, they are indispensable in understanding his complex musical persona.
(Robert Cummings, Rovi, answers.com)