_If the Rays which paint the Colour in the Confine of yellow and orange
pass perpendicularly out of any Medium into Air, the Intervals of their
Fits of easy Reflexion are the 1/89000th part of an Inch. And of the
same length are the Intervals of their Fits of easy Transmission._
This is manifest by the 6th Observation. From these Propositions it is
easy to collect the Intervals of the Fits of easy Reflexion and easy
Transmission of any sort of Rays refracted in any angle into any Medium;
and thence to know, whether the Rays shall be reflected or transmitted
at their subsequent Incidence upon any other pellucid Medium. Which
thing, being useful for understanding the next part of this Book, was
here to be set down. And for the same reason I add the two following
Propositions.