The formation of a subject index to the Alphabetical Catalogue is a matter of much less urgency to the Museum itself, but one of even greater importance to the public. It could not be undertaken without special assistance from the State, but would probably repay its cost in a great degree, and has in any event the very strongest claims upon the support of an enlightened government. It is moreover much less formidable than appears at first sight. We have already explained how the way for a more exact classification has been prepared by arranging one copy of the catalogue in the order of the shelves. The apparent magnitude of the task is further diminished by the following considerations: 1. It requires no cross-references. 2. Titles may be abbreviated to the utmost. 3. It can be temporarily suspended upon the completion of any section. 4. The section of biography is classified already, merely requiring the cross-references from the subjects of biographies to be brought together; and several other extensive sections need not be classified at all. Nobody, at least nobody worth taking into account, wants catalogues of the titles of novels, plays, and sermons. Classified lists of some other subjects, on the other hand, would be of inestimable value, and there is one which, in the interests of the Museum itself, should be undertaken without delay. Among the inconveniences attending the ill-considered removal of the Natural History collections to South Kensington—a measure forced on by the Government against the wish of the working Trustees of the Museum—is the injury likely to be inflicted upon them from want of access to a library. Naturalists cannot study without books any more than without specimens; but the Government which gratuitously created the want seems in no hurry to supply it. The principle of a grant appears indeed to be admitted; but at the rate at which this grant seems likely to be doled out, English Natural Science will be placed at a serious disadvantage for many years. Something may possibly be done by transferring duplicates from Bloomsbury (a question, however, not to be decided in haste), and some anonymous writers in scientific journals have modestly suggested that all books on Natural History might go to Kensington; so that a student of the physiology of colour, for example, would have to read his Wallace at one end of the town and his Tyndall at the other. We should, however, just as soon expect Parliament to decree on similar grounds the cutting of the zoological articles out of the encyclopædias as to enact that the national library of England should be the only professedly imperfect library in the world. Indeed the argument cuts two ways, for if it is fair that the mineral department should have Cresconius Corippus to illustrate its gems, it must be equally fair that the library should have the mineralogist's gems to illustrate its Cresconius Corippus. Until then, the Natural History departments can acquire a library of their own, it must be desirable for them to possess a catalogue of everything relating to their subjects extant in the British Museum. An abridged list, classified according to subject, might be speedily furnished if Government would provide the compilers, and would be an invaluable boon to the scientific world at large, abroad quite as much as in England. Scientific authorities, of course, would be consulted respecting the principles of classification, and we may take this opportunity of repeating that while probably no subject-index has been or can be free from inconsistency and ambiguity, none has ever been too bad to be useful. That a high degree of excellence is attainable is shown by Messrs. Low & Marston's alphabet of subjects to the London Catalogue. The meritorious compiler, we should suppose, can hardly have seen all the books he indexes; yet, so far as we are aware, he has only committed one positive error, the very pardonable one of enumerating Mr. Gosse's "On Viol and Flute" among works on musical instruments.