refracted in the surface AB, and propagated by gikh to the surface EF,
whence it is reflected and refracted again by the surface AB. So that after
two refractions and one reflection, there is propagated a kind of fainter
Ray emnf, whose pulse is not only weaker by reason of the two refractions
in the surface AB, but by reason of the time spent in passing and repassing
between the two surfaces AB and EF, ef which is this fainter or weaker
pulse comes behind the pulse cd; so that hereby (the surfaces AB, and EF
being so neer together, that the eye cannot _discriminate_ them from one)
this confus'd or _duplicated_ pulse, whose strongest part precedes, and
whose weakest follows, does produce on the _Retina_, (or the _optick nerve_
that covers the bottom of the eye) the sensation of a _Yellow_.

And secondly, this _Yellow_ will appear so much the deeper, by how much the
further back towards the middle between cd and cd the spurious pulse ef is
remov'd, as in 2 where the surface BC being further remov'd from EF, the
weaker pulse ef will be nearer to the middle, and will make an impression
on the eye of a _Red_.

But thirdly, if the two reflecting surfaces be yet further remov'd asunder
(as in 3 CD and EF are) then will the weaker pulse be so farr behind, that
it will be more then half the distance between cd and cd. And in this case
it will rather seem to precede the following stronger pulse, then to follow
the preceding one, and consequently a _Blue_ will be generated. And when
the weaker pulse is just in the middle between two strong ones, then is a
deep and lovely _Purple_ generated; but when the weaker pulse ef is very
neer to cd, then is there generated a _Green_, which will be _bluer_, or
_yellower_, according as the _approximate_ weak pulse does precede or
follow the stronger.

Now fourthly, if the thicker Plate chance to be cleft into two thinner