Opticks 1717 - Up

j&cd to the Chart or reflefied back to the
Quick-UVer ) accordingly as, they are in their
Iits of eafy Reflexion or Tranfkilion n$c~~
t]~y arrive at that Surf&et. For the Intervals
of the Fits of the Rays which Ml perpendicu-
~;xrIy on the Speculum, and are retlctted bacl;
in the ike perpendicular Lines, bV r&on of
the equality of thefe Angles and Likes, are of
the fame length and number within the ~lafs
drcr Reflexion as before bv rhc Tgth Prop&.
ticn of the third Part of this Eool;. end tlrer’+
fore fince all the Rays that enter through the
firit Surface are in their Fits of eajy Tranfmi&
iion at their entrance, and as n-~any of thefe as
arc reflerSted by the fecond are in their Fits of
eafy Reflexion there, all thefe muik be again’in
their Fits ‘of eafy TranfmifIion at their return
to the firit-, and by confequence there go out
of the Glafs to the Chart, and form upon it the
nfhite Spot of Light in the center of the Rings,
For the reafon holds good in all forts of Rays,
and therefore all forts muit go out promifcu-i
oufly to that Spot, and by their ,mixturc cauk
it to be white. But the Intervals of the Fits of
thofe Rays which are refle&d more obliquely
than the enter, muit be greater after Retlexion
than be E! ore by the rjth and 20th Propofitions.
And thence it may happen that the Rays at their
return to the fir-it Surface, may in certain Qbfiquities
be in Fits of eafy ReAexion, and return
back to the Quick-filver, and in other intcrmedihte
Obliquities be again in Fits of eafy Tranfmillion,
and fo go out to rhe Chart, and aint
on it the Rings of Colours about the tihite sp poti
T% And