[ 121 J 
From the foregoing obfervations it appears that, 
at the fummer folflice of the year 1690, Ardturus 
was 2 0 40' 12", 8 to the South of the Sun’s center 
in declination: the motion of the liar, in declination, 
from that time to the fummer folflice of the year 
1772, including its proper motion, is 26' 16", 4. 
Ardturus, therefore, in 1772, fhould have been 
3 0 6 ' 29", 2 to the South of the Sun’s center, if the 
angle of the ecliptic and equator had not varied : 
but that diflance was found by adtual obfervation to 
be 51", 6 lefs. By fo much therefore mufl the ob- 
liquity of the ecliptic have become lefs in an interval 
of 82 years; and, confequently, the variation in 
100 years will be da", 92. 
If the obfervations of Ardurus be reduced to the 
folflice of 1771, and the zenith diflance of the Sun’s 
center, as oblerved in that year, be made ufe of in 
the fame manner, the variation of the obliquity in 
81 years will be found — 48", 8, and in 100 years 
= 60". 
If the quantity of the arc of Mr. Flamfleed’s in- 
flrument were accurately known, the obfervations 
which he made at the winter folflice in 1690 might 
be compared with later obfervations, in order to de- 
termine both the quantity of the obliquity in 1690, 
and alfo the variation fince his time. Accordingly, 
I have endeavoured to determine the error of the arc 
of the inflrument between 28° and 75 0 of zenith 
diflance, and proceeded in the following manner. 
I computed feveral obfervations of the flars ^Tauri, 
7 j Ple'iadum, y and ^ Geminorum, and (p, <r , and 
0 Sagittarii, as obferved by Mr. Flamfteed, in the 
years 1690, 1691, and 1692, and reducing them 
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