In the 19th century the science of history underwent a sort of industrial revolution. The machinery of research, invented by the genius of men like Mabillon, was perfected and set going in all the archives of Europe. Isolated workers or groups of workers grew into national or international associations, producing from archives vast collections of material to be worked up into the artistic form of history. The result of this movement has been to revolutionize the whole subject. These men of the factory--devoting their lives to the cataloguing of archives and libraries, to the publication of material, and then to the gigantic task of indexing what they have produced--have made it possible for the student in an American or Australian college to master in a few hours in his library sources of history which baffled the long years of research of a Martene or Rymer. The texts themselves have mostly become as correct as they can ever be, and manuals and bibliographies guide one to and through them, so that no one need go astray who takes the trouble to make use of the mechanism which is at his hand. For example, since the papal archives were opened, so many _regesta_ have appeared that soon it will be possible to follow the letter-writing of the medieval popes day by day for century after century. The apparatus for this research is too vast to be described here. Archives have been reformed, their contents catalogued or calendared; government commissions have rescued numberless documents from oblivion or destruction, and learned societies have supplemented and criticized this work and co-ordinated the results. Every state in Europe now has published the main sources for its history. The "Rolls" series, the _Monumenta Germaniae historica_, and the _Documents inedits_ are but the more notable of such national products. A series of periodicals keeps watch over this enormous output. The files and indices of the _English Historical Review_, _Historische Zeitschrift_, _Revue historique_, or _American Historical Review_ will alone reveal the strength and character of historical research in the later 19th century.