THURSDAY'S sale of modern British and Irish art at Christie's London auction rooms included a number of paintings by Jack B. Yeats, one of which called The Sisters made £150,000. Dublin, Number One Ferry and The Man In The Attic, both also by the same artist, fetched £144,500 and £41,000, respectively. However, three other pictures by Yeats in the same auction remained unsold, as did a portrait of a lady by Sir John Lavery.