Now, what are we to conclude regarding the attempt to elevate to a rank in statistical science, mere estimates of private wealth, for a large portion of which, by the statements of those who make them, no actual statistical data exist? And when this is confessedly the case in our own country, the only one attempting the impossible task of tabulating the wealth of the people, what shall we say of the demand that is made upon our credulity of accepting the guesses of Mr. Giffen, or Mr. Mulhall, as to British wealth? Are we not justified in applying the old Latin maxim--"_De non apparentibus, et de non existentibus, eadem est ratio_," and replying to those who demand of us to know how much any nation is worth, that it is sometimes an important part of knowledge to know that nothing can be known? Among the literally innumerable inquiries liable to be made of a librarian, here is one which may give him more than a moment's pause, unless he is uncommonly well versed in American political history--namely, "What was the Ostend Manifesto?" To a mind not previously instructed these two words "Ostend Manifesto", convey absolutely no meaning. You turn to the standard encyclopaedias, Appleton's, Johnson's Universal, and the Britannica, and you find an account of Ostend, a little Belgian city, its locality, commerce, and population, but absolutely nothing about an Ostend manifesto. But in J. N. Larned's "History for Ready Reference", a useful book in five volumes, arranged in alphabetical order, you get a clue. It refers you from Ostend, under letter O, to Cuba, where you learn that this formidable Ostend manifesto was nothing more nor less than a paper drawn up and signed by Messrs. Buchanan, Mason, and Slidell, Ministers of the United States to Great Britain, France, and Spain, respectively, when at the watering-place of Ostend, in 1854, importing that the island of Cuba ought to, and under certain circumstances, must belong to the United States. Looking a little farther, as the manifesto is not published in Larned, you find the text of the document itself in Cluskey's "Political Text-Book", of 1860, and in some of the American newspapers of 1854. This is a case of pursuing a once notorious, but more recently obscure topic, through many works of reference until found. In many searches for names of persons, it becomes highly important to know before-hand where to look, and equally important where not to look, for certain biographies. Thus, if you seek for the name of any living character, it is necessary to know that it would be useless to look in the Encyclopaedia Britannica, because the rule of compilation of that work purposely confined its sketches of notable persons to those who were already deceased when its volumes appeared. So you save the time of hunting in at least one conspicuous work of reference, before you begin, by simply knowing its plan.