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 The advantage of this does not, I hope, require much exposition. I will only make one remark. Every student knows the vast difference which is made when you have some right to assume the completeness of any research. I may look into books, and search libraries on the chance of finding information indefinitely. But if I have a book or a library of which I can say with some confidence that, if it is not there, the presumption is that it does not exist, my labour has a definite, even though it be a negative, result. That, for example, is the sufficient justification of the collection of every kind of printed matter in the British Museum. It is not only that nobody can say beforehand what bit of knowledge may not turn out to be useful, but that one has the immense satisfaction of knowing that a fact not recorded somewhere or other on those crowded shelves must be, in all probability, a fact for which it is idle to search further. No biographical dictionary can be in the full sense exhaustive; an exhaustive dictionary would involve a reprint of all the parish registers, to mention nothing else; but it may be approximately exhaustive for the purposes of all serious students of any of the various departments of history. In a great number of cases, moreover,