[ io8 ] 



The fame method may be ufed in taking the 

 Moon's diftance from a fixed flar. 



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-obfervation, 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 (hew the principles on which thefe directions 

 are founded. 



Obfervers are commonly told, that in making the 

 fore obfervation they mould 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 j and when the Sun touches the 

 horizon at the lowed part of the arch defcribed by him 

 the quadrant will mew 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- 

 poffible, the precept is incomplete. Moreover, in 

 taking the Sun's altitude in or near the zenith, this 

 rule entirely fails, and the beft 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 purpoie. We have thus twa 

 rules for the fame thing, v/hich is a proof that nei- 

 ther of them is an univerfal one, or fufficient in all 

 cafes .alone. 



In 



