AS1R0GN0SY. 27 



^returns, and Aldebaran, and as in modern times has been 

 mcontrovertibly proved with respect to many others. The 

 bright star Arcturus has, during the 2100 years (since the 

 times of AristLlus and Hipparchus) that it has been ob- 

 «erved, changed its position in relation to the neighboring 

 fainter stars 2£ times the moon's diameter. Encke remarks 

 ' that the star a Cassiopeia appears to have moved Z\ lunar 

 diameters, and 61 Cygni about 6 lunar diameters, if the an- 

 cient observations correctly indicated its position." Conclu- 

 sions based on analogy justifyjis in believing that there is 

 every where progressive, and perhaps also rotatory motion. 

 The term " fixed stars" leads to erroneous preconceptions ; 

 it may have referred, in its earliest meaning among the 

 Greeks, to the idea of the stars being riveted into the crys- 

 tal vault of heaven ; or, subsequently, in accordance with 

 the Roman interpretation, it may indicate fixity or immo- 

 bility. The one idea involuntarily led to the other. In Gre- 

 cian antiquity, in an age at least as remote as that of Anax- 

 imenes of the Ionic school, or of AlcmsBon the Pythagorean, 

 all stars were divided into wandering {aorpa TtXav&ueva or 

 TrkavrjTd) and non-wandering fixed stars (dnXavelg dorepeg 

 or dnXavrj aorpa) .* Besides this generally adopted desig- 

 nation of the fixed stars, which Macrobius, in his Somnium 

 Scipionis, Latinized by Sphcera aplanes,i we frequently 

 meet in Aristotle (as if he wished to introduce a new tech- 

 nical term) with the phrase riveted stars, evdedeu&va aorpa, 

 instead of dnXavri,$ as a designation for fixed stars. From 

 this form of speech arose the expressions of sidera infioca 

 ccdo of Cicero, Stellas quas putamus affixas of Pliny, and as- 



* Pseudo-Plut., De plac. Philos., ii., 15, 16; Stob., Eclog. Phy$, } p 

 682 ; Plato, in the Timceus, p. 40. 



t Macrob., Somn. Scip., i., 9-10 ; slellce inerrantes, in Cicero, De A'jC. 

 Deorum, iii., 20. 



% The principal passage in which we meet with the technical expres 

 sion kvdedefieva darpa, is in Aristot., De Coslo, ii., 8, p. 289, 1. 34, p. 290, 

 1. 19, Bekker. This altered nomenclature forcibly attracted my atten- 

 tion in my investigations into the optics of Ptolemy, and his experi- 

 ments on refraction. Professor Franz, to whose philological acquire- 

 ments I am indebted for frequent aid, reminds me that Ptolemy {Syn- 

 tax, vii., 1) speaks of the fixed stars as affixed or riveted; uairep 7rpo- 

 OTTefyvKOTeq. Ptolemy thus objects to the expression afyalpa dirXavi]s 

 (orbis inerrans) ; " in as far as the stars constantly preserve their rela 

 tive distances, they might rightly be termed dn^avetq; but in as far aa 

 the sphere in which they complete their course, and in which they seem 

 to have grown, as it were, has an independent motion, the designation 

 anlavijc is inappropriate if applied to the sphere." 



