Close — Cosmograpliical Tractate in the Irish Language. 461 



Arabic texts of Messahalah before them. Grerard gives us " hathara,''^ 

 without explanation, in three places. It is evident that he did not 

 know what this meant, and therefore simply copied it in Eoman letters 

 fi'om the Ai-abic original. But as the Irish translator gives in this 

 place rotJi (the Irish for wheel), it is clear he had rota before him in 

 Latin B. This shows that the writer of Latin B, must have had before 

 him in his Arabic exemplar, not the corrupt and unmeaning hathara 

 but the proper Arabic word for wheel. 



Perhaps Messahalah's most remarkable departui'e from the ideas of 

 Ptolemy occurs in his mode of producing the precession of the equi- 

 noxes. Ptolemy held that this was caused by the eastward pro- 

 gressive turning of the sphere of the fixed stars, at the slow rate of 1° 

 in a hundred years. Messahalah gives this progressive motion to the 

 stars, at the same rate ; but he also makes the equinoctial points and 

 zodiacal signs move retrogressively along the ecliptic ; though at what 

 rate he does not say. This latter would have been peremptorily rejected 

 by Ptolemy ; as it would involve, of course, a movement of the Earth 

 which he altogether repudiated; besides giving too great a relative 

 motion between the stars and the equinoctial points. Messahalah 

 doubtless did not perceive this consequence, for he also did not believe 

 in the mobility of the Earth. It is evident that he was misled by some 

 apparently (not reaUy) mutually inconsistent statements of Hipparchus 

 on this question, as he is presented to us by Ptolemy in the "Almagest," 

 Book YII., Chaps. 1, 2, 3 (see last paper on Hipparchus). 



Others have erred as well respecting the belief of Hipparchus on 

 this subject, and most probably for the same reason. One group of 

 distinguished astronomers and historians of astronomy tell us that 

 Hipparchus explained the precession (solely) by the progression of the 

 fixed stars ; another equally distinguished group tell us that he 

 explained it (solely) by the retrogradation of the equinoctial points ; 

 one of these groups is, of course, quite mistaken on this question. 

 Messahalah has Fracastor with him in his mistake of using a quite 

 unnecessary sphere to carry the equinoctial points backwards. 



The explanation of this seems to be that Messahalah was among 

 the very earliest "Arabian" astronomers to whom the "Almagest" 

 was accessible in an Arabic translation. Haroun Alraschid ordered a 

 translation of it (probably more than one) in the earlier part of 

 Messahalah's career. The work, as might be expected, was found at 

 first very diificult, and the results unsatisfactory ; and it was not until 

 A.D. 827, that a sufficiently good translation was published at the 



