COMETS. 541 



which bent backwards, 10 form the tails, from the observations 

 of Hensius (1744), Bessel, Struve, and Sir John Herschel. 

 Besides the magnificent Comet of 1843, 11 which could be seen 

 by Bo wring in Chihuahua (N.W. America) as a small white 

 cloud from nine o'clock in the morning until sunset, and by 

 Amici, in Parma, at full noon, 1 23' eastward of the Sun, !a 



10 This formation of the tail at the anterior part of the 

 comet's head, which has occupied Bessel's attention so much, 

 was the opinion of Newton and Winthrop (compare Newton's 

 Principia, p. 511, and Philos. Transact, vol. Ivii. for the year 

 1767, p. 140, fig. 5). Newton considered that the tail was 

 developed most considerably and longer near the Sun, be- 

 cause the cosmical ether (which we call with Encke the 

 resisting medium) was the densest there, and the particulce 

 caudce, strongly heated and supported by the ether, ascended 

 more easily. Winthrop considered that the principal effect 

 did not take place until some time after the perihelion pas- 

 sage, because, according to the law established by Newton 

 (Principia, pp. 424 and 466), the maxima are universally re- 

 tarded (in periodical changes of heat as well as in ocean tides). 



11 Arago, in the Annuaire pour 1844, p. 395. The obser- 

 vation was made by the younger Amici. 



18 With regard to the Comet of 1843, which appeared with 

 unexampled splendour in Northern Europe during the month 

 of March, near Orion, and approached nearer to the Sun than 

 any hitherto observed and calculated comet, all the details 

 are collected in Sir John Herschel's Outlines of Astronomy, 

 589-597 ; and in Peirce, American Almanac for 1844, p. 42. 

 On account of physiognomical resemblances whose uncertainty 

 was already shown by Seneca (Nat. Qu&st. lib. vii. caps. xi. 

 and xvii.), it was at first considered to be identical with the 

 comets of 1668 and 1689 (Cosmos, vol. i. p. 128, note; Galle, 

 in Gibers' Cometenbahnen, nos. 42 and 50). Boguslawski 

 (Schum. Astr. Nachr. No. 545, p. 272) believes, on the con- 

 trary, that its previous appearances were, with a revolution of 

 147 years, those of 1695, 1548, and 1401 ; he even calls it the 

 Comet of Aristotle, " because he traces it back to the year 371 

 before our era, and together with the talented Hellenist Thiersch 

 of Munich, considers it to be a comet which is mentioned in 



