EPOCHS IN THE HISTORY OF THE CONTEMPLATION 



xnents in instruments for angular measurements, and by 

 their zealous endeavours to correct the earlier tables by 

 careful comparison with the heavens. Sedillot has recog- 

 nised in the seventh book of the Almagest of Abul-Wefa 

 the important inequality in the moon's motion, which 

 vanishes at the Syzygies and Quadratures, and has its greatest 

 value at the Octants, and which under the name of " variation" 

 has long been regarded as a discovery of Tycho Brahe. ( 352 ) 

 Ebn-JumVs observations at Cairo have become particularly 

 important for the perturbations and secular changes of the 

 orbits of the two great planets, Jupiter and Saturn. ( 353 ) 

 A measurement of a degree of the meridian, executed by the 

 orders of the Caliph Al-Mamun in the great plain of 

 Sindschar between Tadmor and Rakka, by observers whose 

 names have been preserved to us by Ebn-Junis, is less 

 important for its result than for the evidence which it affords 

 of the scientific cultivation of the Arabian race. 



We must also attribute to this cultivation, in the West, 

 the astronomical congress held in Toledo in Christian Spain 

 under Alphonso of Castile, in which the Eabbi Isaac Ebn 

 Sid Hazan occupied a prominent place ; and in the far East, 

 the Observatory provided with many instruments established 

 by Ilschan Holagu, the grandson of Ghengis-khan, on a 

 mountain near Meragha, in which Nassir-Eddin of Tus in 

 Khorasan made his observations. These details are deserv- 

 ing of notice in the history of the contemplation of the 

 Universe, because they remind us in a lively manner of what 

 the Arabians have effected in the extension of knowledge 

 over wide portions of the earth's surface, and in the accu- 

 mulation of numerical results : results which contributed 

 materially in the great epoch of Kepler and Tycho Brahe to 





