[ I0 7 ] 
time in the diftances of the Sun from that ftar (the 
motion of the ftar in declination being allowed for 
during that interval of time), will be the quantity 
by which the Sun will have approached to or have 
receded from the ftar. If the ftar were abfolutely a 
fixed point, and the obfervations fufticiently nu- 
merous, that, by taking a mean, the neceftary and 
unavoidable errors in obfervation might either be 
confiderably diminifhed or almoft annihilated, the 
method might be pradlifed to great advantage. But 
as the ftar (Ardturus) had a proper motion, and its 
apparent place was continually varying from the effedt 
of the nutation of the earth’s axis , as the limb of 
the Sun was fometimes approaching to, and fome- 
times receding from, the ftar, by a kind of libratory 
motion from the efFedt of the nutation ; alfo and as 
the obliquity of the ecliptic itfelf was, in all proba- 
bility, continually diminishing ; from a combination 
and as it were involution of thefe motions no cer- 
tain conclufion could be drawn, fince, in the fpace of 
a few years, the apparent obliquity may be the fame, 
and yet the mean obliquity may have diminifhed, 
or perhaps, in the fpace of a few years, the obliquity 
may appear to have increafed, when it may really 
have become lefs. Whereas, by reducing the ob- 
fervations to their mean pofition, and by afligning to 
each known caufe its proper and allowed efFedt, a 
regularity and uniformity muft neceflarily take place, 
as far at lead: as is confident with the unavoidable 
errors in obferving. 
Mr. Caftini, in the Memoirs of the Academy of 
Sciences for 1767, acquaints us, that, in 1748, the 
apparent diftance of Ardturus from the upper limb 
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