THEORIES OF EXCENTRICS AND EPICYCLES. 295 



says, that it is not necessary to assume so remote a period ; 

 for the computation may be made from the beginning of the 

 treta acre, at which instant all the moveable points of the 

 heaven's were again in conjunction in Mesha, except the 

 apogees and ascending nodes, which must therefore be 

 computed from the creation. The present Hindoo astrono- 

 mers, therefore, go no farther back than the call yug in de- 

 termining the mean longitudes. 



For the equation of the centre a trigonometrj' is re- 

 quired. This is given in the Surya Siddhanta, and it is 

 one of the most curious and interesting parts of the treatise : 

 it will be described in the sequel. 



To account for the apparent unequal motion of the 

 planets, which they suppose to move uniformly in their 

 orbits, they have recourse to excentric circles, and deter- 

 mine the excentricity of the orbits of the sun and moon 

 ■with respect to that circle, in which they place the earth as 

 the centre of the universe, to be equal to the sines of their 

 greatest anomaUstic equations. The Hindoos in this agree 

 whh the ancient Greek astronomers, but their calculation is 

 very different. They substitute an epicycle instead of the 

 excentric, which cornes to the same, but, what is peculiar 

 and difficult to explain, they make the radius of this epi- 

 cycle vary at ever\- degree, which thus goes on diminishing 

 from 0= to 90^ of anomaly. Indeed it is not the radius 

 which they make truly to vary, but the circumference of the 

 epicycle ; thus they render the calculation needlessly com- 

 plex. There is another singularity ; although the equation 

 of the moon is more than double that of the sun, the varia- 

 tions of their epicycles are sensibly the same. Thus, like 

 the Greeks, the Indians have their theories of excentrics 

 and epicycles ; but instead of calculating by the rigorous 

 rules of trigonometry, they have introduced an empirical 

 term for which there' is neither reason nor necessity. The 

 \-ulo-ar anions the Bramins believe that eclipses are occa- 

 sioned by the monster Rohere, and they join to this idea 

 others equally tainted with ignorance and absurdity. This 

 belief being founded on declarations contained in works 

 supposed of divine authority, which no pious Hindoo can 

 call in question, some astronomers have been cautious in 

 explaining the passages in these books which do not accord 

 with the principles ot' their science. They have justified as 



