Soo Dr. maskelyne’s Account of 
contrary limbs of the Sun, crolfing one another at the 
focus of the telefcope under an angle equal to that ot 
the Sun’s diameter, the union of the limbs of the two 
images of the Sun cannot appear perfedt unleis the eye 
be difpofed to fee objects diftindtly which are placed at 
point of interfedtion. But if the eye be difpofed to fee 
objects diftindtly, which are placed nearer the object - 
glafs than the interfedtion is, the two limbs will appear 
feparated by the interval of the axes of the pencils in 
that place; anti if the eye be difpofed to fee objects dif- 
tindtly, which are placed farther from the object-glafs 
than the interfedtion is, the two limbs will appear to en- 
croach upon each other by the diftance of the axes of the 
pencils, after their croffing, taken at that place. 
To explain this, let ov (plate XIX. fig. i.) reprefent 
the centres of the two femi-circular glafles of the objedt- 
glafs micrometer, feparated to the diftance ov from each 
other, fubtending the angle oav, equal to the Sun’s dia- 
meter, at the point a, which is the common focus of the 
two pencils of rays having o a and v a for their axes, 
namely, thofe proceeding from contrary fides of the Sun, 
and paffing through the contrary femi-circles ; and let d 
be the eye-glafs. It is evident, that if d be properly 
placed to give diftindt vifion of objedts placed at the point 
a, the rays oa,va, as well as all the other rays belonging 
