SEQUEL TO THE EPOCH OF HIPPARCHUS. 181 



cumbrous Sexagesimal Arithmetic of the Greeks, and introducing the 

 notation by means of the digits 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, which we 

 now employ. 45 These numerals appear to be of Indian origin, as is 

 acknowledged by the Arabs themselves ; and thus form no exception 

 to the sterility of the Arabian genius as to great scientific inventions. 

 Another improvement, of a subordinate kind, but of great utility, was 

 Arabian, being made by Albategnius. He introduced into calculation 

 the sine, or half-chord of the double arc, instead of the chord of the 

 arc itself, which had been employed by the Greek astronomers. There 

 have been various conjectures concerning the origin of the word sine ; 

 the most probable appears to be that sinus is the Latin translation of 

 the Arabic word gib, which signifies a fold, the two halves of the chord 

 being conceived to be folded together. 



The great obligation which Science owes to the Arabians, is to 

 have preserved it during a period of darkness and desolation, so that 

 Europe might receive it back again when the evil days were past. 

 We shall see hereafter how differently the European intellect dealt 

 with this hereditary treasure when once recovered. 



Before quitting the subject, we may observe that Astronomy brought 

 back, from her sojourn among the Arabs, a few terms which may 

 still be perceived in her phraseology. Such are the zenith, and 

 the opposite imaginary point, the nadir ; — the circles of the sphere 

 termed ahnacantars and azimuth circles. The alidad of an instru- 

 ment is its index, which possesses an angular motion. Some of the 

 stars still retain their Arabic names ; Aldebaran, Rigel, Fomalhaut ; 

 many others were known by such appellations a little while ago. 

 Perhaps the word almanac is the most familiar vestige of the Arabian 

 period of astronomy. 



It is foreign to my purpose to note any efforts of the intellectual 

 faculties among other nations, which may have taken place independ- 

 ently of the great system of progressive European culture, from which 

 all our existing science is derived. Otherwise I might speak of the 

 astronomy of some of the Orientals, for example, the Chinese, who are 

 said, by Montucla (i. 465), to have discovered the first equation of the 

 moon, and the proper motion of the fixed stars (the Precession), in 

 the third century of our era. The Greeks had made these discoveries 

 500 years earlier. 



« Mont. i. 376. 



