Some fifty years ago the science of comparative philology began to make itself felt, and Celtic scholars tried to apply its principles to Celtic. Pritchard, Bopp, Diefenbach, Pictet, and others worked in the right direction, but they failed fully to solve the Celtic problem. J. Caspar Zeuss, a Bavarian Highlander, at last succeeded, by combining with a mind of unusual power a devotion to the subject which amounted well-nigh to a sacrifice of his life. This devotion might not even have been sufficient if he had not possessed what no one before him possessed—the really oldest manuscripts of both the Irish and Welsh dialects. The labours of Zeuss have shown:—That the Gaelic and Welsh languages were originally one; that dialectic differences in Cæsar’s time were so small that an old Gael would be at once understood in Wales; and that the Gaels and Cambrians were identical with the Celts of the Continent—with those of Spain, Gaul, Lombardy, and the Alpine countries; that this Celtic tongue is one of the branches of the Aryan stock of languages. The consequence of these established facts is to put an end to all attempts at connecting the Celtic with the Semitic class of tongues. We know the Gaelic language now in three stages:— 1. Old Gaelic up to 1000 A.D. The most ancient relics of this period are the glosses of St. Gall in Switzerland, the Ambrosian Library of Milan, &c., discovered by Zeuss. 2. Middle Gaelic, from 1000-1500 A.D., is represented by an extensive mass of manuscript literature. 3. Modern Gaelic from the sixteenth century, when books began to be printed, to the present day. The softening caused by excessive aspiration is the greatest change which the language has undergone. As spoken in Scotland at the present day the chief dialectic differences are:— 1. The _ia_ of the North for the _eu_ of the South and West Highlands, illustrated by BIAL, BEUL, _mouth_; FIAR, FEUR, _grass_. 2. The vowel-tone difference, illustrated in such words as ORAN, song. The _o_ is pronounced in three different ways; in Islay and other parts of Argyll like _o_ in _old_; in Mull and other place like _ou_ in _foul_; in the North generally like _aw_ in _law_. 3. The consonantal difference illustrated in the pronunciation of _c_ and _chd_. 4. The accentual or rhythmic tone difference, observed in the conversation of natives of different places. In Arran and Perthshire, and to some extent in Caithness and Sutherland, the people in speaking cut off the terminal syllables of many words. In the North Highlands they speak with a slow, sometimes swinging emphasis; in the South Highlands they are more hurried in their utterance. Any Highlander, speaking distinctly, will be readily understood, North and South.