COMETS. 189 



For the explanation of what has been said above of the re- 

 mark of Chinese astronomers on the occasion of their observ- 

 ation of the Comet of March, 837, in the dynasty of Thang, 

 I insert here a translation from Ma-tuan-lin of the verbal 

 statement of the law of direction of the tail. It is said there, 

 "In general, the tail of a comet which is situated eastward 

 from the Sun is directed toward the east, calculating from 

 the nucleus ; but if the comet appears to the west of the Sun, 

 the tail turns toward the west."* Fracastoro and Appia- 

 nus say, still more correctly, "that a line produced through 

 the head of a comet in the direction of the axis of the tail 

 meets the Sun." The words of Seneca are also characteristic : 

 " The tails of comets fly from the Sun's rays." {Nat. Qucest., 

 vii., 20.) While, among the yet known planets and comets, 

 the periods of rotation dependent upon the half-major axis, 

 the shortest and the longest of the planets, are in the propor- 

 tion of 1 : 683, the proportion in the case of the comets is as 

 1:2670. Mercury (87d - 97) is here compared with Neptune 



circumstance that, like some other astronomers, he characterizes the 

 first year before the Christian era as anno 0. It is to be observed, in 

 conclusion, that Sir John Herschel assumes for the Comet of 1843, seen 

 in full daylight near the Sun, an entirely different period of revolution, 

 one of 175 years, which leads to the years 1668, 1493, and 1318, as the 

 dates of its previous appearances. (Compare Outlines, p. 208-372, with 

 Galle, in Olbers's Cometenbahncn, p. 208; and Cosmos, vol. i., p. 137.) 

 Other combinations by Peirce and Clausen lead to periods of revolution 

 of even 214 or 74 years: a sufficient proof how hazardous it is to trace 

 back the Comet of 1843 to the archonship of Asteus. The mention of 

 a comet under the archonship of Nicomachus, in the Meteorol., lib. i., 

 cap. vii., 10, has at least the advantage of showing us that this work 

 was written when Aristotle was at least 44 years of age. It has al- 

 ways appeared to me remarkable that the great man, as he was already 

 14 years old at the time of the earthquake at Achaia, and of the appear- 

 ance in Orion of the great comet with a tail 60° in length, should speak 

 with so little animation of so brilliant an object, and content himself 

 with enumerating it among the other comets " which had appeared in 

 his time." The astonishment incx-eases when, in the same chapter, the 

 statement is found that he had seen with his own eyes something misty, 

 even a feeble haza (k6/j.tj), round a fixed star in the hip-bone of the Dog 

 (perhaps Procyon in the small Dog), (Meteorol., i., 6, 9). Aristotle also 

 speaks (i., 6,11) of his observation of the occultation of a star in Gemini 

 by the disk of Jupiter. With regard to the vaporous or nebulous en- 

 velope of Procyon (?), it recalls to my mind a phenomenon of which 

 frequent mention is made in the old Mexican annals according to the 

 Codex Tellerianvs. " This year," it is said there, " Citlalcholoa smoked 

 again;" this is the name of the planet Venus, also called Tlazoteotl in 

 the Aztec language (see my Vncs des Cordilleres, torn, ii., p. 303) : this 

 is probably, in the Grecian as well as the Mexican sky, a phenomenon 

 of atmospheric refraction — the appearance of small halos. 



* Edward Biot, in the Comptes Rendus, torn, xvi., 1843, p. 751. 



