460 Proceedings of the Royal Irish Academy. 



allowable in them and interesting. But their handling of the latter 

 subject is decidedly inferior scientifically to that of Alfergani, a later 

 contemporary of Messahalah, and of Albatani, Trho came two or three 

 generations later. A small number of the improprieties in the present 

 tractate are of a very remarkable character ; some, however, are only 

 of the natui'e of blunders, the matter in hand beiag given correctly 

 elsewhere. 



We shall now make a few remarks on some of the salient points in 

 the tractate under consideration. 



It is interesting to observe that ]\ressahalah, who looks up to 

 Ptolemy as " the Philosopher," and his honoui'ed master, departs from 

 the teaching of his preceptor on several points, sometimes even while 

 appealing to his authority. For instance, ia Chapter 18, Messahalah 

 gives a demonstration that the Sun is larger than the Earth. He gives 

 this demonstration as Ptolemy's ; but Ptolemy's is quite different, and 

 vastly superior. 



Again, it is evident that Ptolemy regarded the fixed stars as 

 shining by their own proper light; but Messahalah, in Chapter 21, 

 and elsewhere, speaks of those stars, as shining by reflected sunlight. 

 In this he is countenanced by Isidore of Seville, Albertus Magnus, 

 and incredible as it may seem, even by Copernicus himself ; to these 

 we may add (from Piccioli) Metrodorus, Albatani, Yitellio, Eeinhold, 

 Blancanus and Scheiner. So that Messahalah eiTs herein in very good 

 company. 



In Chapter 22 Messahalah shows most correctly that we may have 

 an annular eclipse of the Sun, but Ptolemy states that the angular 

 diameter of the Moon is never less than that of the Sun ; which would 

 make such an eclipse impossible. Here Messahalah has the advantage 

 over his master. 



In Chapter 27, he refers to Ptolemy as positing ten spheres for 

 canying the planets and stars round the Earth ; but Ptolemy mentions 

 only eight ; one for each of the seven planets (including the Sun and 

 Moon), and one for the fixed stars. 



In Chapter 27, Messahalah gives what is really an illustration fi"om 

 a potter's wheel, which was proposed by Cleomedes, to explain the 

 compounding of the dii'ect or eastward proper motions of the planets 

 with the westward daily rotation of the firmament. This illustration, 

 however, he assigns to Ptolemy. 



By the way, we seem to have, in this same chapter, an interesting 

 proof, that Gerard of Sabbionetta, who wrote Latin A, and the writer 

 of Latin B, fi'om whom the Iiish translator worked, had different 



