The facts of O’Brien’s life have never been set in order. Even the date of his birth in County Limerick is uncertain. His untimely death was at Cumberland, Virginia, from wounds in the Federal service early in the Civil War. The clearest impression of the man may be had from William Winter’s introduction to a collection of his verse and prose, published in Boston, 1881. He seems very like the Thackeray Irishman--generous, impulsive, extravagant with money and words. In the geniality that deserved their warm affection his somewhat Bohemian companions found a touch of genius; but the demands of a spendthrift life hand-to-mouth, and the facility with which these demands could be met, both made against the realisation of this higher promise. That it remained only a promise may be ascribed also to his dying at thirty-four. Youth is evident especially in that his prose is imitative. Poe is suggested almost immediately; and there is often an undertone of Dickens, the Dickens of the Christmas stories. In other aspects, too, O’Brien’s writing is the work, not of a craftsman, but of a brilliant amateur. The fancies that he threw upon the periodical press are never quite achieved. Considered as materials, these fancies vary in value all the way from the conceptions of _The Diamond Lens_ and _The Wondersmith_, which are not far from pure imagination, to _Tommatoo_ and _My Wife’s Tempter_, which are mere melodrama. But whatever their potential value, O’Brien’s hand was not steady enough to bring it out. The main scene of _The Diamond Lens_, the microscopic vision, is as delicate as it is original, and as vivid as it is delicate; but the preparation for it is fumbling, and the solution unsatisfying. The tale printed below is exceptionally compact in structure and careful in detail. The obvious general resemblance to Poe’s tales of physical horror should not obscure certain original merits. The note of realism, for instance, is not merely Poe’s verisimilitude; it expresses a differentiation of character more like that of Kipling’s similar study, _The End of the Passage_. Prof. Brander Matthews (_Philosophy of the Short-Story_, page 68) points out the similarity in conception of Maupassant’s _Le Horla_. Writing much prose and verse for many magazines now long passed away, and a play or two for Wallack, O’Brien found his steadiest employment with the Harpers between 1853 and 1858, and his most congenial life with the younger journalists and artists of New York. WHAT WAS IT? A MYSTERY [_From “Harper’s Monthly Magazine,” March, 1859; volume xviii, page 504. The signature is Harry Escott_]