This Figure therefore I here represent, is
wholy _Hypothetical_.
Let ABCDHFE in the sixth Figure be a _frustum_ of _Muscovy-glass_, thinner
toward the end AE, and thicker towards DF. Let us first suppose the Ray
aghb coming from the Sun, of some remote luminous object to fall
_obliquely_ on the thinner plate BAE, part therefore is reflected back by
cghd, the first _Superficies_; whereby the perpendicular pulse ab is after
reflexion propagated by cd, cd, equally remote from each other with ab, ab,
so that ag + gc, or bh + hd are either of them equal to aa, as is also cc,
but the body BAE being transparent, a part of the light of this Ray is
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_.
Pages:
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193