[ 9 4 ] 
tice of by many aftronomers : in particular, Dr. Hal - 
ley mentions it in N° 355 of the Philofopbical Trans- 
actions : Mr. CaJJini , in the Memoirs of the Aca- 
demy of Sciences for 1738, p. 231, has fhewn, that 
there is a variation of jive minutes in the latitude of 
that ftar between his own time and that of Tycho, 
in an interval of a century and a half : and M. le 
Mounter , in the Memoirs of the Academy of Sciences 
for 1767, p. 417, proves, that the latitude of Ardurus 
varies at the rate of two feconds every year j and that 
the longitude decreafes at the rate of 6o // in a hun- 
dred years *. But as an inquiry as well into the true 
quantity as into the direction of this motion has not 
hitherto been made public, I propofe to give fome 
account of my own obiervations made exprefsly with 
this view in the years 1767 and 1768, with a tranfit 
inftrument of 44'inches, and a moveable mural qua- 
drant of 33 inches, both conftruded by Mr. Bird, 
and of the conclulions refulting from a companion 
between them and fome obfervations made by Mr. 
Flamfteed in 1690. 
It may perhaps be objeded, that the differences of 
right afcenlion, as determined by Mr. Flamfteed’s 
mural inftrument, are not to be depended upon from 
the very nature of his inftrument. Mr. Flamfteed 
was himfelf too good an obferver not to be aware of 
this ; and accordingly in the Prolegomena to the 
third volume of the Hijioria Ccelejlis , p. 132, he in- 
forms us in what manner he determined the error of 
* See alfo the Memoirs of the Academy of Sciences for 
1769, p. 21. See alfo Aftronomiae Fundamenta, by the Abbe 
de la Caille; who, in reducing his obfervations of Arcturus, 
fuppofes the annual motion of declination in that ftar — 
p., 169, and 187. 
the 
