C 108 ] 
The fame method may be ufed in taking the 
Moon’s diftance from a fixed ftar. 
It may not be amifs here to make fome remarks 
on the rules that have been ufually given for ob- 
ferving the Sun’s altitude, both with the fore and 
back- obfer vation, which have all been defective, and 
to point out the proper directions to be followed, 
when a telefcope is not ufed with two parallel wires 
to direct the quadrant perpendicular to the horizon, 
and to fhew the principles on which thefe directions 
are founded. 
Obfervers are commonly told, that in making the 
fore obfervation they fhould move the index to 
bring the Sun down to the part of the horizon di- 
rectly beneath him, and turn the quadrant about 
upon the axis of vifion ; and when the Sun touches the 
horizon at the lo weft part of the arch defcribed by him 
the quadrant will fhew the altitude above the vifible 
horizon. I allow that this rule would be true, if a 
perfon could by fight certainly know the part of the 
horizon exaCtly beneath the Sun ; but, as this is im- 
poflible, the precept is incomplete. Moreover, in 
taking the Sun’s altitude in or near the zenith, this 
rule entirely fails, and the belt obfervers advife to hold 
the quadrant vertical, and turn one’s felf about upon 
the heel, flopping when the Sun glides along the 
horizon without cutting it : and it is certain that this 
is a good rule in this cafe, and capable with care of 
anfwering the intended purpofe. We have thus twa 
rules for the fame thing, which is a proof that nei- 
ther of them is an univerfal one, or fufficient in all 
cafes alone. 
In 
t Jej 
