C “7 J 
ing glafs ; for although the furfaces of a glafs may 
be parallel, yet there always arifes fome little con- 
fufion from the double reflection. Neither will 
the Moon appear too weak by two unfilvered re- 
flections, even when her crefcent is very fmall, 
except fhe fhould be hazy or clouded ; and then 
the light may be increafed by lowering the te- 
lefcope fo as to take in part of the fllvered re- 
flection of the index-glafs, which in this cafe 
mult be uncovered : the fame is alfo to be under- 
flood with refpeCt to the Sun, fhould his light be 
too much weakened by hazinefs or thin clouds. 
The horizon- glafles fhould be adjufted, or the error 
of adjuftment found by the Sun or Moon ; the firft 
will be in general the beft objeCt for the purpofe ; 
and, as the Sun or Moon feen direCtly through the 
unfilvered part of the horizon-glafs will be much 
brighter than the image of the fame feen by two 
unfilvered reflections, it muft be weakened by a v dar- 
kening glafs placed beyond the horizon-glafs, the 
reflected image being farther weakened, if neceffary, 
by a paler darkening glafs placed in the ufual man- 
ner between the index-glafs and the horizon-glafs. 
If a quadrant was defigned principally for taking 
the diftance of the Moon from the Sun and fixed ftars, 
and was not wante i for obferving terreftrial angles, 
it would be the beft way to have none of the glafles 
fllvered, but to leave the horizon glafles intirely tranf- 
parent, and to put a red glafs for an index-glafs of 
the fame matter with the darkening glafles, which 
would refleCt light from the fore-furface only. 
The Sun’s altitude might alfo be obferved with this 
inftrument, either by the fore or back-obfervation 
and 
