is Memoir on the Diminution of the 
<¢ The astronomer Tsou-tchong determined this solstice, 
and it is the first Chinese solstice the determination of 
which we find detailed. Here it is: On the day Gin-su of 
the }0th moon, noon shadow ten feet seven-inches seven fen 
five li. On the day Ting-ouey of the 11th moon, noon 
shadow ten feet eight inches one fen seven li five hao. 
On the day Vou- chin, 1)th moon, noon shadow ten feet 
seven inches five fen two or three li. 
«The first of January »462 was Ting-yeou ; - therefore 
Gin-su was the 27th of November 461: Ting-ouey the 11th 
of January 462, and Vou-ching the 12th of January 462. 
<« Tsou- tchong examined the difference in the shadows of 
the 11th and 12th of January, and by the rule of three 
that he uses, be found between the 11th and 12th of Ja- 
nuary, the moment when the nogn shadow was equal to 
the noon shadow of 27th of November: he computed the 
days ke, fen, between that moment and the noon of 27th 
of November: he halved it, which he added to the noon of 
the 27th of November, and he thus found this solstice to be 
the 30th of December at 31 ke after midnight, or 75 26’ 24” 
of the morning. Until the Jesuits’ arrival, the Chinese 
astronomers have made use of this method to ascertain the 
solstices, 
«¢ The gnomon’s length was eight fect :—the foot is ten 
inches ; thea inch, ten li; the li, ten hao. 
“ Tsou- tchong took great precautions to have the gno- 
mon perpendicular. The plane was levelled, and he mea- 
sured exactly the shadow ; he wanted to correct the errors 
of Hoching- tien’s method, According to that method, 
the solstice of the year 461 should have taken place on he 
day Kia-ching (19th December), 7° 19” afternoon. The 
solar year of Hoching-tien was 365 days 24 ke 60’ Ti", 
or 5! 53’ 44”. Tsou-tchong undertook to show the 
errors of this computation, and said that the solar year was 
of 365 days 5° 49'40”. He does not say upon what ob- 
servations he founded this determination. This author also 
corrected the time of the solstice of the year 173; which’ 
he determined on the 22d of December, at g" 7’ of the 
morning.’ 
The observations on which Tsou -tchong founded his de- 
termination are evidently this salstice of 173, and the one he 
determined in 4615 for the interval of these two solstices, 
such as Tsou- tchong has determined them, 1 is of 288 solar 
revolutions, and of 288 Julian years, wanting two days one 
hour 40’ 36"; which gives for the year’s length 365 days 
5" 49° 39” , the same within 1” as Tsou-tchong’s. 
If 
