4 Memoir on the Diminution of the 
fixing the moment of the solstice at the middle of thz in- 
terval of time clapsed between the two equinoxes, or be- 
tween the two moments when the two shadows before and 
after the solstice were equal. It is casy to perceive that he 
fixed forthe summer solstice half an hour too Jate ; and for 
the winter, as much too soon; so that the errors of the 
Tables at the summer valet should exceed those of the 
winter solstice by about 2’ 27”, This is in fact the case, 
very nearly, in the p ain observations. The mean error 
in the preceding observations is for the winter solstice 5”, ot 
for the summer, 2! 191: thus the mean error of the six 
preceding observations is 1’ 12",5: dividing: it by 521, the 
number of VEN elapsed from 1279 to 1800, the quotient 
r4” wil] be the amount of what the secular motion of the 
sun should be increased, according to. the preceding sol- 
stices; which would dimini sip the year’s length about 
3",5. The above-related observations of lengths ‘of shadows 
about the equinoxes give — 3,6 for the mean error of the 
Tables, after the spring equinox, and + 1'3”,7 for the 
error before the autumn’s equinox: so that the mean 
error of the Tables given by these observations is 60”,1> 
and it should be remarked that this error is independent of 
the one that may have been committed in the equator’s 
situation 3 from which results an increase of about 11° in 
the secular motion of the sun. However it be, the small- 
ness of these errors proves the goodness of the observations, 
and makes us regret that we have not a greater number. 
We see in the History of Chinese Astronomy of Father 
Gaubil, published by Father Sauciet, p. 72, 3d part, that in 
ths winter solstice of the year 1280, Cocheou- King deter- 
mined the sun’s position in theconstellation Hiu of 318°,1075. 
Chinese, that is to say, distant 321°,1075 from the com- 
mencement of the constellation Hiu, This censtellation 
commences at the star 6 of Aquarius; so that the solstice: 
was, according to Cocheou- King, distant from that star 
321°,1075 Chinese. This astronomer, and generally all the. 
Ghinese astronomers until the Jesuits’ arrival, have divided 
the circumference into degrees, so that each degree repre~ 
sented the mean daily motion of the sun. This degree 
thus varied like the duration which they gave to the solar 
year ; and Cocheou-King made it 365 days 2425, which 
reduces the 321°,1075 Chinese to 316? 29’ 58” sexagvesimal, 
The longitude of 6 of Aquarius for the Ist January 1281, 
and calculated by the formulas of vol. iii. of my Méc. Céd. 
is 10° 30° 9’ 15"; the winter solstice was then- distant 
346° 35' 45"; Cocheou- King’s error was, therefore only 
6! AT, which j is yery inconsiderable. ARAB. 
