Obliquity of the tlctipiic. 433 



fcong's determination. This difference will appear very 

 small, when we consider the uncertainty of the precise 

 epocha of the observation on which this determination is 

 founded, and above all the uncertainty even of the -observa- 

 tions. It would suffice to remove 54 years beyond the UOOdth 

 before our aera > to reduce this difference to nothing, and 

 then the observation would belong to the time of Ou-en- 

 ouang, father of Tcheou-Kong, Whom Father Gaubil men- 

 tions as having much loved and cultivated astronomy. The 

 Chinese astronomers determined the moment of the solstice* 

 by observing equal lengths of the gnomons' shadows forty 

 or fifty days previous and after the solstice; and from 

 that there may already be some error inTcheou-Kong's de- 

 termination. But the greatest error that is to be appre- 

 hended in the observation is in the manner of referring the 

 solstice to the stars, in order to which the moment of the 

 passage of such stars as crossed the meridian twelve hours after 

 the moment of the solstice was observed: thus the right 

 ascension of the opposite point to the summer solstice 

 would be determined, and therefore also that of the win- 

 ter solstice. But for so doing it was necessary to measure 

 an interval of twelve hours. It appears that hour-vessels 

 were used for measuring the time that a vessel was in fill- 

 ing to different heights with the water falling from a higher 

 vessel (Treatise of Chinese Astronomy of Father Gaubil, 

 published by Father Sauchet, Part I. p. 37.) It is easy to 

 perceive how uncertain this manner of measuring time was, 

 and three minutes of time, in an interval of twelve hours, 

 are sufficient to account for the error of Tcheou-Kong's 

 determination. The Chinese astronomers made likewise 

 use of the moon's situation relatively to the star3 in the 

 lunar eclipses, to obtain the place of the sun, and therefore 

 that of the winter solstice, at which they fixed the com* 

 mencement of their year. 



We must come down a thousand years, from Tcheou- 

 Kong's epocha, before we find a second observation of the 

 gnomons' shadows made in the solstices in China. Towards 

 the year 104 before our aera, the astronomers Lieou-hiang and 

 Lo-hia-hong observed the length of the shadow of an eight- 

 feet gnomon at the winter and summer solstices. They 

 found it 13 feet one inch four fen, or 13ft, 14 at the 

 former, and one foot Cive inches eight fen, or lft,58 at 

 the latter (vol. ii. of Chinese History, published by Father 

 Sauchet, p. 8). This observation is supposed to have been 

 made in the town of Siganfou, then the capital of the em- 

 pire : but this is an error which Father Gaubil has rectified 



Vol. 36. No. 152. Dec. 1810. 2 E in 



