[ SII ] 
to continual returns : and I fatisfied myfelf, that the 
plane of the fe(5tor never deviated above three minutes 
from the meridian in any of the obfervadons taken on 
the South fide of the hill, which, it is evident, could not 
in the lead: atfe^l the obferved zenith dillances of ftars* 
I hardly ever obferved without examining the bife6tion 
of the point at the centre of the inftrument, by the plumb- 
line; which was abfolutely neceflary, on account of the 
gradual changes of the wooden frame. My view in 
mentioning thefe minute cireumftances is, to caution fu- 
ture obfervers, as well as to confirm my own obferva- 
tions. But whoever makes ufe of an inftrument of this 
kind, fupported on a wooden frame, will find the greateft 
attention neceflary to attain the fame degree of accuracy 
in his obfervadons, as if his inftrument were fixed to an 
immoveable wall. In the mean time, by obfervadons 
taken with the quadrant and tranfit inftrument, I got a 
meridian line, and planted a pole to preferve it on the 
top of the hill, to the South of the inftrument, and ano- 
ther at the foot of the fame hill ; from whence, by mea- 
furing off an equal diftance to the Eaft (as the South-weft 
corner of the obfervatory lay to the Eaft of the tranfit 
inftrument) and fetting up another pole, another meri- 
dian line was got, pafllng through the South-weft cor- 
ner of the Southern ftation of the obfervatory. The rea- 
fon for making the meridian line pafs through the South- 
weft corner of the obfervatory rather than through the 
middle of it was, that this part of it had been taken when 
VoL. LXV. Yyy the 
