Another highly instructive test of the correctness of his theory may be derived from the investigations of Lhuyd himself, who, in his comparison of the Welsh and Irish languages, uniformly distinguished the current terms from the obsolete synonymous words that occur only in ancient MSS. This comparison proves distinctly that the Irish and Welsh languages approximate, as we ascend, at a rate which, if as rapid previously as we know it to have been up to the date of the earliest MSS., would imply that these languages must have been identical about the era of the Roman invasion. As the changes which languages undergo in their infancy are more rapid than those which occur at later stages of their growth, it is possible that the unity of these Tongues may be ascribed even to a much later period, an opinion which has been maintained by a very judicious and excellent writer, Mr. Edward Davies, who in his “Claims of Ossian” has published an early specimen of Irish Poetry, which in Language and Style he regards as identical with the most ancient productions of the Welsh Bards. Making every allowance for the irregularity of the changes which occur in Languages, I do not conceive it possible that the Welsh and Irish could have differed very essentially in the time of Cæsar. This leads directly to another conclusion, viz. that the first colonization of Ireland could not have taken place a great many centuries before the Roman invasion. Had such been the case, the differences between the Welsh and Irish Languages must have been proportionately more extensive. In the time of the Romans we learn that an Irish traitor arrived in Britain, who stated that Ireland might be kept in subjection by a single legion, an incident which tends, however slightly, to favour the opinion that the sister Island was at that period but thinly, perhaps because but recently, peopled. Of the extent of the changes which the Celtic languages have undergone since the first arrival of the Celts in Europe, we possess proofs of far more ancient date than the earliest literary specimens of the living dialects of the Celtic in the Local names of Celtic regions, as preserved in Roman Maps, and in the existing languages of the French, English, and other nations, who occupy countries of which the Celts were the first inhabitants. These names I shall show to consist of three elements: A union of 1, Welsh, Cornish, &c.; 2, Irish, Highland Scotch, &c.; and 3, Terms not extant in any Celtic Tongue, but preserved in the Oriental, Greek, and other languages.