[ r 93 ] 
west of Greenwich. I have here made ho al- 
lowance for the difference of power of the two-feet re- 
fleCtor, ufed at Jupiter’s inlet, and the fix-feet refleCtor ? 
ufed at Greenwich ; becaufe the mean is taken be- 
tween the refults frfim the immerfions and emerfions i 
which method includes that correction ; that is to 
fay, gives the fame refult whether that correction be 
made or not. From the foregoing comparifons it 
fliould feem that the air is much clearer at the ifland 
of anticosti than at Greenwich, which Mr. 
weight confirmed to me, fince the immerfions 
give the longitude only greater than the emer- 
fions; which fhews that Mr. wright obferved an 
immerfion only 4" fooner, and an emerfion as 
much later, with a two feet refleCtor, than was 
done at Greenwich in a fix feet refleCtor ; although, in 
an equally good air, this latter telefcope would have 
had the advantage of the former by 20" inftead 
of 4". 
Vol. LX1V. 
C c 
XXVI. Extras, l 
