Obliquity of the Ecliptic. 13 
Tf x is called the altitude of the equator at Nankin ; y the 
number into which the variation of the declination 1s to 
be multiplied, corresponding with 10’ of increase in the 
sun’s longitude; lastly, if x design an increase in the obli- 
quity of the ecliptic, Tsou-tchong’s observations give us 
the following equations: 
_ &— 21° 39' 59” = y° 1’ 41,0— x 0,90669=306° 18’ 51” 
r—21 42, 48,54 y° 1 41,0—% 0,90676=36 12 48 
Z—21 39 25,74 y' 1 44,7 —% 0,90093=36 21 21 
which three equations give 2 = 57° 56’ 55”, + 2° 0,90527, 
giving the latitude of Nankin = 32° 3’ 5” — 2% 090527. 
According to Father Fontauey’s observation, the latitude 
of Nankin 1s 32° 4’: comparing it with the preceding, we 
shall have 2 = — 10”,7; but the observations being sus- 
ceptible of an error of 1’, and the town of Nankin being 
go very extensive that the difference of latitude of its ex- 
treme points is much greater, these observations may be 
considered as agreeing with the formulas of Méc. Cél. 
The ecliptic’s obliquity as given by the formulas of Méch. 
Cél. was then 23° 39’ 8”,9; it was then, by Tsou-tchong’s 
observation, 23° 38’ 8",2. Supposing z = 0, we shall have 
y = — 1,12850, « = 57° 58’ 8". 
This value of x differs little from the preceding. The 
value of 7 seems to indicate, like that of the preceding 
observation, a diminution in the sun’s longitude as given 
by the Tables. But the modern observations do not admit 
of that diminution. However it be, Tsou-tchong’s obser- 
vations deserve so much the more confidence, as that ex- 
perienced observer’s intention having been to correct the 
errors of his predecessors, he took special care to make 
them accurately. Besides, it was to the solstice determined _ 
by those observations that Cocheou-king has compared his 
own observations, in order to obtain the year’s length, 
which he found of 365 days 24¢5, the same exactly as our 
Gregorian year. 
We find that in the year 629, an observation was made 
carefully by an experienced astronomer, with the intention of 
correcting an error of his predecessors. ‘ It has been seen in 
the second observation,” says Father Gaubil, (Conn. desTems 
for 1809, p.357,) * that Litchun-foung had objected against 
the solstitial shadows improperly applied to Siganfou. This 
astronomer was therefore desirous of observing exactly the 
‘noon shadow of the solstices at Siganfou with an eight-foot 
gnomon. He made his observation the year Ki-tcheou (629) 
ef Tching-Koan’s empire in the town of Tchang-gou, or 
; 9 Siganfous 
