the existence of the verb tiachinoa=to burn up the fields or forests, and of the noun tlachi-noliztli=the act of burning up or scorching the fields or forests, and finally, metaphorically, tlachinoli-teuotl=war or battle=destruction. It is only when we thus realize all the natives could express by the image of an eye, looking through a circle, that we begin to grasp its full meaning when employed as a symbol in their picture writings. As to the obsidian mirror, which undoubtedly was the symbol of Tezcatlipoca and, consequently, must have pertained to his representative, the priest of the Night, we find that it played a most prominent rôle in the cult he presided over. In the first case it appears as though it was resorted to in Mexico as in the conquered province of Guatemala, as the oracle which rendered final judgment. A series of illustrations, etc., to be published in my final work on the Calendar System, will prove satisfactorily that the Mexican astronomers extensively employed black obsidian mirrors as an aid to astronomical observations, by means of reflection. Besides mirrors on the summits of temples and mountains, certain square columns, placed on an elevation and faced with a broad band of polished obsidian, are pictured in some Codices. It is obvious that the latter in particular, if carefully oriented, would have served as an admirable means of registering the periodical return of planets, stars or constellations to certain positions; they would then be reflected on the polished surface, as in a frame. In certain Codices the double, tau-shaped courtyard or enclosure surrounded by a high wall with battlements, which was employed in the daytime for the national game of ball, figures in combination with obsidian mirrors. I draw attention to the fact that the name of these courtyards was tlach-tli, which literally means the looking place=the observatory and that, amongst the edifices of the great temple, a tezca-tlachtli=obsidian-mirror-observatory, is described. I shall demonstrate more fully, on another occasion, that the chief purpose of these enclosures was to serve as astronomical observatories. Dr. Brinton, Señor Troncoso and other authorities have already observed that the game of ball itself was intended to represent the idea of the perpetual motion of the heavenly bodies. (See American Hero-myths, p. 119.)