[ 4<S* ] 
colleding the coloured Lights: And this will like- 
wife happen, when the white heterogeneous Light 
of the bright Ring or Band does penetrate and con- 
found the Rays of the Halo, now fomewhat weak- 
ened. It is plain, that in order to a genuine Expli- 
cation of Mock-Suns, it is chiefly requifite to have 
a clear Notion of the Origin of the horizontal Ring, 
or Bands. And from Huygens's Experiment with a 
cylindric Glafs full of Water expofed to the Sun, 
which produces a white horizontal Ring by Reflexion 
alone, without an opake Nucleus ; he aflerts that 
the horizontal Bands, that interfed the folar Coronet 
are formed, when cylindric frozen Vapours are 
fufpended about the Sun, chiefly where the Halo is 
depided, in a Situation perpendicular to the Hori- 
zon ; which being redilinear, each of them exhibits 
by Reflexion a lucid Line equal to the Sun’s Dia?- 
meter ; and feveral of thefe optic Lines joining, com- 
pofe the Plane of the Ring or Band. 
His laft Sedion is fpent in explaining the Appear- 
ance ol Part of an inverted Iris , which accompanied his 
Mock-Suns: In order to which, he thus accounts 
for a (common or) primary Rainbow. 
A primary Iris is formed, when the Sun's Rays 
falling on Drops of Rain, after fufFering Two Re- 
fradions, and One Reflexion, tend to the Eye in fuck 
a Dircdion, that the Axis of the Iris , coming di- 
redly from its Centre, and palling by the Eye to 
the Sun, makes with thefe Rays returning from the 
Drops, an Angle of 40 Degrees below, and of 4a 
Degrees above ; whereby the Width of the Iris is 
2 0 1 5 and its Diameter 42° 17'. 
But as this inverted Iris was but One Degree broad, 
and the Diameter of the Arch probably but half that 
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