CXV111 NOTES. 



( 498 ) p. 324. Compare the ideas of Sir John Herschel on the position of 

 our planetary system, Kosmos, Bd. i. S. 157 and 415 ; and Struve, Etudes 

 d'Astronomie Stellaire, 1847, p. 4. 



(<) p. 324. Apelt says (Epochen der Geschichte de Menschheit, Bd. i. 

 1845, S. 233) : " The remarkable law of the distances, which usually passes 

 under the name of Bode's law (or that of Titius), was a discovery of Kepler's, 

 who, after many years of persevering industry, first deduced it by calculation 

 from the observations of Tycho de Brahe." See Harmonices Mundi, libri 

 quinque, cap. 3. Compare also Cournot, Additions to a Translation of Sir 

 John Herschel, Traite d'Astronomie, 1834, S. 434, p. 324, and Fries, Vorle- 

 sungen iiber die Sternkunde, 1813, S. 325 (Law of the distances in the 

 secondary planets or satellites). The passages from Plato, Pliny, Censorinus, 

 and Achilles Tatius, in the Prolegomena to the Aratus, are carefully collected 

 in Fries, Geschichte der Philosophic, Bd. i. 1837, S. 146150 ; in Martin, 

 Etudes sur le Timee, T. ii. p. 38 j and in Brandis, Geschichte der Griechisch- 

 Romischen Philosophic, Th. ii. Abth. i. 1844, S. 364. 



O p. 325. Delambre, Hist, de 1'Astronomie moderne, T. i. p. 360. 

 ( 501 ) p. 325. Arago, in the Anuuaire for 1842, pp. 560564 (Kosmos, 

 Bd. i. S. 102 ; English translation, Vol. i. p. 88). 



C 08 ) p. 326. Compare Kosmos, Bd. i. S. 142148, and 412 (English 

 translation, Vol. i. p. 127-133, Notes, 9192.) 



f 608 ) p. 327. Annuaire du Bureau des Longitudes pour 1'an 1842, 

 p. 312 353 (Etoiles changeantes ou periodiques). In the seventeenth 

 century there were recognised as variable stars, besides Mira Ceti (Holwarda, 

 1638) and a Hydrse (Montanari, 1672), Persei or Algol, and % Cygni (Kirch, 

 1686). On what Galileo calls nebulae, see his Opere, T. ii. p. 15, and Nelli, 

 Vita, Vol. ii. p. 208. Huygens, in the Sistema Saturninum, points in the 

 dearest manner to the nebula in the sword of Orion, in saying of nebulae 

 generally : " Cui certe simile aliud nusquam apud reliquas fixas potui animad- 

 vertere. Nam ceterce nebulosse olim existimatse atque ipsa via lactea, perspi- 

 cillis inspectse, nullas nebulas habere comperiuntur neque aliud esse quam 

 plurium stellarum congeries et frequentia." This passage shews that 

 Huygens (as previously Galileo) had not attentively considered the nebula in 

 Andromeda which Marius had first described. 



O p. 329. On the important law, discovered by Brewster, of the con- 

 nection between the angle of complete polarisation and the refractive power 

 of bodies, see Philosophical Transactions of the Royal Society for the year 

 1815, pp. 125159. 



