By a curious paradox, language is one of the most changeable and one of the most permanent facts in European history. It is changeable in that it can be quickly learned or unlearned, especially from one generation to another, as is convincingly illustrated by European immigrants to the United States. It is permanent in that the line of demarcation in the open country shows surprisingly little variation over a period of several centuries. Hence it is highly important to distinguish conditions in the towns and among the more conservative peasant population. As regards the open country, the linguistic frontier between French and German shows very slight changes since the Middle Ages, when it was fixed in each region by the relative preponderance of the Latin-speaking Gauls or of the Teutonic invaders. Slight advances of German in the Middle Ages and of French since the sixteenth century are traceable at certain points, but are relatively unimportant. The present line of division has never been absolutely determined, but a local study was made by C. This in 1886 and 1887 on the basis of personal examination, and his results have been generally accepted by both French and German scholars. The line follows the political frontier, here the crest of the Vosges, only for about sixty miles in Upper Alsace. In the south it includes two districts to the east, Eteimbes and Montreux, while it dips still farther to the east in the upper valleys of the Weiss and the Breusch and the middle valley of the Liepvrette, all of these districts speaking French. In Lorraine the linguistic frontier lies well to the east of the political boundary, running in a zigzag fashion from Mount Donon to the northwest across the open country through or near Sarrebourg and southwest of Thionville to the Luxemburg boundary. About 6 per cent of the area of Alsace and about 46 per cent of the area of Lorraine thus contain a French-speaking majority.