The catalogue was now (August 1839) fairly commenced under the immediate personal direction and responsibility of Mr. Panizzi. Mr. Jones, however, held from the first a primacy among the assistants actually engaged in its compilation, which became enhanced as the difficulties of the task became more apparent from day to day. It had been supposed that the old titles might pass with slight examination: they proved to require the most careful revision; and the work of the revisers needed to be in its turn revised. Subject to a reference to Mr. Panizzi in extreme cases, Mr. Jones was the ultimate authority. His clear head, legal habit of mind, and attention to minute bibliographical accuracy, rendered him invaluable in this capacity, and his decisions constitute the basis and most essential part of the body of unprinted law which unforeseen exigencies gradually superinduced upon the original rules. He also took a leading part in the revision of the proofs. The causes of the suspension of the printing of the catalogue have been so fully treated by the writer in a paper at the Cambridge meeting of the Library Association, that it is needless to enter upon them here. It made no difference to the amount of Mr. Jones's labours, except as regarded the correction of the press. He continued to work upon the catalogue and also upon the supplementary catalogue of books added to the library, both as reviser and as general supervisor, until he became Keeper of Printed Books in 1856. His other duties were numerous and important: he exercised, in particular, the immediate control of the attendants, a responsibility the more onerous in proportion to the continual increase of the establishment. In 1843 he was engaged along with Mr. Watts in collecting the materials on which Mr. Panizzi based his famous report on the deficiencies of the library, which ultimately occasioned so large an increase in the annual grant. In 1849 he prepared for the Royal Commission that crushing exposure of Mr. J. P. Collier's notions of short and easy methods of cataloguing which should be especially valued by librarians, as it is perhaps the best practical illustration to be found anywhere of the difficulties attaching to the correct bibliographical description of a book. He was also enabled to devote some attention to literature. About 1842 he wrote a large number of articles for the Dictionary of Universal Biography, edited by Mr. George Long for the Society for the Diffusion of Useful Knowledge, a great and meritorious undertaking, unfortunately not carried beyond letter A, although the continuation as far as BE was actually in type. Mr. Jones's articles chiefly treated of obscure or forgotten writers, and required much research. He also contributed to the _Quarterly_ and _North British_ Reviews; his article in the latter on the British Museum Library (1851) is the best account of its administration to be found anywhere. He carried on an extensive correspondence with Mr. Wilson