The first observation of the phenomenon may have been made two or three years prior to this period; but, notwithstanding, the merit of having (in the spring of 1683) been the first to investigate the phenomenon in all its relations in space is incontestably due to Dominicus Cassini. The light which he saw at Bologna in 1668, and which was observed at the same time in Persia by the celebrated traveler Chardin (the court astrologers of Ispahan called this light, which had never before been observed, 'nyzek', a small lance), was not the zodiacal light, as has often been asserted,* but the p 140 enormous tail of a comet, whose head was concealed in the vapory mist of the horizon, and which, from its length and appearance, presented much similarity to the great comet of 1843. [footnote] *Dominicus Cassini ('Mém. de l'Acad.', t. viii., 1730, p. 188), and Mairan ('Aurore Bor.', p. 16), have even maintained that the phenomenon observed in Persia in 1668 was the zodiacal light. Delambre ('Hist. de l'Astron. Moderne', t. ii., p. 742), in very decided trms ascribes the discovery of this light to the celebrated traveler Chardin; but in the 'Couronnement de Soliman', and in several passages of the narrative of his travels (éd. de Langlès. t. iv., p. 326; t. x., p. 97), he only applies the term niazouk (nyzek), or "petite lance," to "the great and famous comet which appeared over nearly the whole world in 1668, and whose head was so hidden in the wewst that it could not be perceived in the horizon of Ispahan" ('Atlas du Voyage de Chardin', Tab. iv.; from the observations at Schiraz). The head or nucleus of the comet was, however, visible in the Brazils and in India (Pingré, 'Cométogr.', t. ii., p. 22). Regarding the conjectured identity of the last great comet of March, 1843, with this, which Cassini mistook for the zodiacal light, see Schum., 'Astr. Nachr.', 1843, No. 476 and 480. In Persian, the term "nizehi âteschîn"(fiery spears or lances) is also applied to the rays of the rising or setting sun, in the same way as "nayâzik," according to Freytag's Arabic Lexicon, signifies "stellæ cadentes." The comparison of comets to lances and swords was, however, in the Middle Ages, very common in all languages. The great comet of 1500, which was visible from April to June, was always termed by the Italian writers of that time 'il Signor Astone' (see my 'Examen Critique de l'Hist. de la Géographie', t. v., p. 80). All the hypotheses that have been advanced to show that Descartes (Cassini, p. 230; Mairan, p. 16), and even Kepler (Delambre, t. i., p. 601), were acquainted with the zodiacal light, appear to me altogether untenable. Descartes ('Principes', iii., art. 136, 137) is very obscure in his remarks on comets, observing that their tails are formed "by oblique rays, which, falling on different parts of the planetary orbs, strike the eye laterally by extraordinary refraction," and that they might be seen morning and evening, "like a long