Archdeacon Pratt on Chinese Astronomical Epochs. 3 



shadows is liable. It then appears that the latitude and the 

 obliquity, determined from these observations, will be free from 

 error only within the limits — 0°*25 and + o, 25, that is, within 

 a range of o, 5. Now this variation in the obliquity, at the 

 rate of 48" \n a century, is equivalent to a range of SO'xGO 

 -i-48" = 37^ centuries ! This astronomical observation, therefore, 

 really gives no independent information whatever regarding its 

 date. All we can gather is, that if History points out that 1100 

 B.C. was the era when this observation was made, Astronomy 

 presents no obstacle to this determination. 



On the determination of the Era 2357 B.C. 



4. An attempt has been made by M. Biot (see Journal des 

 Savants, 1840, 1859) to fix the date of the Emperor Yao by 

 reconstructing the celestial sphere (as he imagines it to have 

 been at that time), and reasoning from the change in the posi- 

 tion of the equinoxes. He fixes the date at 2357 B.C. I will 

 briefly explain his process, and then show in what I think it 

 inconclusive. He states that the ancient Chinese astronomers 

 divided the equator into 28 unequal parts (called sieu or man- 

 sions) by declination circles drawn through certain stars chosen 

 for the purpose. M. Biot has evidently bestowed much atten- 

 tion on the subject, and has endeavoured to identify these stars, 

 which the ancient Chinese astronomers are supposed to have 

 used so far back as 4000 years ago ! In the next page, in Tables 

 I. and II., I have gathered together some of his results, and in 

 the two following pages some further calculations, the use of 

 which will be explained. 



In Table I. are given the names of these twenty-eight stars, 

 and their positions at the era, and the consequent widths of the 

 mansions. (The figures in the second column show the magni- 

 tudes of the stars.) In the choice of stars two things surprise 

 one : (1) that their intervals in M are so very unequal, and (2) 

 that in many instances such unimportant stars are chosen. Thus, 

 while the width of the fifth mansion is more than 30°, the width 

 of the third is less than 3°. Indeed the stars at the beginning 

 and end of the third mansion are so near in M } that in the 

 column of longitudes for 1750 a.d. the fourth star falls behind 

 the third ! For this reason apparently M. Biot goes far back 

 into time past for his epoch, that the line joining the two stars 

 may have as large a projection as possible on the equator of the 

 time, so as to give the greatest advantage to this, at best, very 

 ill-conditioned mansion. The fourth is also a narrow mansion, 

 though not quite so narrow as the third. It will be seen that it 

 is the introduction of the star \ Orion (instead of some other, 

 perhaps between Nos. 4 and 5) which makes these mansions so 

 narrow. 



B2 



