That the material has been duly sifted, to the extent of the author's ability, need hardly be said, for the canons of historical composition are now too well settled and too generally understood to allow of any wanton negligence on the part of the writer, or any willing credulity on that of the reader. The one thing essential to the value of such a composi tion is a strict conformity with facts, as far as these can be ascertained. No one expects from it the artistic harmony, the unity and completeness, the agreement of form and substance, which give their highest charm to products of the pure imagination.