Besides these published sources there is the fund of information possessed by public men and the "well-informed" of various grades. Unfortunately this is rarely accessible, or only under conventional restrictions. Here and there I have been able to make use of it without any breach of trust; and to those who have enlightened my darkness I am very grateful. The illumination, I know, is only partial; but I hope that its effect, in respect to the twilight of diplomacy, may be compared to that of the Aurora Borealis lights. After working at my subject for some time, I found it desirable to limit it to events which had a distinctly formative influence on the development of European States. On questions of motive and policy I have generally refrained from expressing a decided verdict, seeing that these are always the most difficult to probe; and facile dogmatism on them is better fitted to omniscient leaderettes than to the pages of an historical work. At the same time, I have not hesitated to pronounce a judgment on these questions, and to differ from other writers, where the evidence has seemed to me decisive. To quote one instance, I reject the verdict of most authorities on the question of Bismarck's treatment of the Ems telegram, and of its effect in the negotiations with France in July 1870.