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difficulty, and the difference of right afcenfioii and 
declination of any two ftars or other points in the 
heavens may be thereby accurately meafured, let the 
difference of right afcenfion be what it will, provided 
the difference of declination does not exceed the 
extent of the fcale of the micrometer ; and thus the 
objeft-glafs' micrometer is put pretty much on a 
footing with the common micrometer, even with rc- 
fpeiff to the meal'uring right afcenfions and de- 
clinations. 
The difference of right afcenfion and declination 
between Venus or Mercurv and the Sun’s limb, in 
their tranhts over the Sun, are to be oblerved nearly 
in the fame manner as the difference of right afcenfion 
and declination of two dars. But the procefs will 
perhaps be rendered clearer, by the following de- 
icription. 
1. Turn the moveable wires E W, N S, into 
fuch a pofition that the Sun’s North limb n (fee 
fg. II.) or the planets North Ikiib V may run along 
the wire E W, which thereby becoaaes a tangent to 
the “peripheries of their difes. 
2. The femicircular glaffes being feparated to a 
convenient diftance, turn the micrometer about, till 
the two images of the planet V, 'u,. pafs over the 
horary wire N S at the fame inftant. 
3. Separate the glaffes of the micrometer to that 
diftance, that the North limb V of the Northernmoft' 
image of the planet may touch the wire E W at the 
fame time that the Northernmoftlimb ofthe South- 
ernmoft image of the Sun touches the fame wire;, 
and the fcale of the micrometer will diew the 
difference of declination of the Northern limbs of 
the. 
