Opticks 1717 - Up

e 2 ‘99 I
to+ of an Inclias 34386 to 34385, :43d+3+383,
34382, refpdtivdy. !~.nd thereford if the thick-
nefs in all thefe cai’es .be $ of an Inch (as it is in
the CMi of which the Speculum VU: made)
the bright Light of the 34389th Ring fllall e-
merge where the Sine of Kefi--aBidri is r17i,
and that of the 34384th, ~84383th and 34382th
Ring where the Sine is 1699, 2031, 2nd 2345
refpeAively. And in thefe Angles of Refra-
&ion the Light of thefe Rings lhall be pl;opagated
from the Speculum to the Charr, and there
paint Rings about the white central round Spot
of Light which we faid was the Light of the
34386th Ring. And the Semi&meters of thcfe
Rings fhall fubtend. the Angles of RefraAion
made at the concave Surface of the Speculum,
and by conkquence their Diameters &all be to
the di+nce,of the Chart from the Speculum as
thofe Sines of Refia&ion doubled are to the
Radius, that is, as 1172, 1659, 2031, and 2345,
doubled are to IOOOOO. And therefore if the
‘diftance of the Chart horn the concave Zknfke
of the SpeceIum be fix Feet (as it was in the
third of thefe Obfervations) the Diameters of
the Rings of this bri.&t yellow Light upon the
Chart fllall be 1’688, 2’389, 2’925 3’375 hches:
For thefe Diameters are to fix Feet, as the a-
bovemention’d Sines doubled are tQ the Ra-
&us. Now khefe Diametkis of the sright YC~low
Rings, ,thus found by computation i;e the
very fame with thofe found in the third of. there
Obfervations by meafuring them ‘, w%. with
z;, 2;;, and 3: Inches, and thkreforc the
$&ory of deriving thefe Rings from the thick-
T4 Y’ nef5 .