262 Dr. Maskelyne’s Attempt to explain 
to me without fcintillation, and as a fmall round circle of fire 
of a fenfible magnitude. If I look at them without the con- 
cave glafs, or with one not fuited to my eye, they appear to 
call: out rays of a determinate figure, not exafllv the lame in 
both eyes, fomewhat like branches of trees (which doubtlefs 
arife from fomething in the confcruflion of the eve) and to fcin- 
tillate a little, if the air be not very clear. To fee day objects 
with moil diflindlnefs, I require a lefs concave lens by one de- 
gree than for feeing the liars bell by night, the caufe of which 
feems to be, that the bottom of the eye being illuminated by the 
day objefls, and thereby rendered a light ground, obfcures the 
fainter colours blue indigo and violet in the circle of diffipa- 
tion, and therefore the belt image of the objefl will be found 
in the focus of the bright yellow rays, and not in that of the 
mean refrangible ones, or the dark green, agreeable to New- 
ton’s remark, and confequently nearer the retina of a fhort- 
lighted perfon ; but the parts of the retina furrounding the 
circle of diffipation of a liar being in the dark, the fainter co- 
lours, blue, indigo, and violet, will have fome fhare in form- 
ing the image, and confequently the focus will be fhorter. 
The apparent diameter of the flars here accounted for is dif- 
ferent from that explained by Dr. Jurin, in his Effay on 
diflinft and indiflindl vifion, arifing from the natural conftitu- 
tion of the generality of eyes to fee obje£ls moft diftinfl at 
moderate diflances, and few being capable of altering their 
conformation enough to fee diflant objects, and among them the 
celeflial ones, with equal diflinflnefs. But the caufe of error, 
which I have pointed out, will affefl all eyes,, even thofe which 
are adapted to diflant objects. 
If this attempt to fhew the compatibility of the adual 
diftindnels of our fight with the different refrangibility of 
light 
