AriTUOGNOSY. 27 



Arcturus," and Aldcbaran, and as in modern times has been 

 incontrovcrtibly proved with respect to many others. The 

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

 times of Aristilhis and Hipparehus) that it has been ob- 

 served, changed its position in relation to the neighboring 

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

 " that the star f-i Cassiopeia) appears to have moved 3i lunar 

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

 cient observations correctly indicated its position." Conclu- 

 sions based on analogy justify us 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 Alcmaion the Pythagorean, 

 all stars were divided into ivandering {liorpa irXavdyfieva or 

 nXavrjrd) and non-icandering fixed stars {airXavelg dorepeq 

 or dnXavf] dor pa). ^ Besides this generally adopted desig- 

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

 Scipionis, Latinized by Sph(xra aiolanes,^ we frequently 

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

 nical term) with the phrase riveted stars, evdeSufieva darpa, 

 instead of dnXavrj,'^ as a designation for fixed stars. From 

 this form of speech arose the expressions of sidera mjixa 

 ccelo of Cicero, Stellas qtcas p)utci'imis ajjixas of Pliny, and as- 



* Pseudo-Plat., Da plac. Philos., ii., 1.5, IG ; Stob., Eclog. Phys., p. 

 582; Plato, in the Timcens, p. 40. 



t Macrob., Somn. Scip., i., 9-10 ; slellce inerrantes, in Cicero, De Nat. 

 Deornm, iii., 20. 



I The principal passage in which we meet with the technical expres- 

 sion kvdtdefj.£va uarpa, is in Aristot., De Caclo, 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; loairep Tzpo- 

 GaEcpvKOTEq. Ptoleuiy thus objects to the expression a<palpa aT:7\,avfi(, 

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

 tive distances, they might rightly be termed dTz7iav£Lq; but in as far as 

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

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

 anT^.avijq is inappropriate if applied to tiie sphere." 



