inform'd.
_Qu._ 16. When a Man in the dark presses either corner of his Eye with
his Finger, and turns his Eye away from his Finger, he will see a Circle
of Colours like those in the Feather of a Peacock's Tail. If the Eye and
the Finger remain quiet these Colours vanish in a second Minute of Time,
but if the Finger be moved with a quavering Motion they appear again. Do
not these Colours arise from such Motions excited in the bottom of the
Eye by the Pressure and Motion of the Finger, as, at other times are
excited there by Light for causing Vision? And do not the Motions once
excited continue about a Second of Time before they cease? And when a
Man by a stroke upon his Eye sees a flash of Light, are not the like
Motions excited in the _Retina_ by the stroke? And when a Coal of Fire
moved nimbly in the circumference of a Circle, makes the whole
circumference appear like a Circle of Fire; is it not because the
Motions excited in the bottom of the Eye by the Rays of Light are of a
lasting nature, and continue till the Coal of Fire in going round
returns to its former place? And considering the lastingness of the
Motions excited in the bottom of the Eye by Light, are they not of a
vibrating nature?
_Qu._ 17. If a stone be thrown into stagnating Water, the Waves excited
thereby continue some time to arise in the place where the Stone fell
into the Water, and are propagated from thence in concentrick Circles
upon the Surface of the Water to great distances. And the Vibrations or
Tremors excited in the Air by percussion, continue a little time to move
from the place of percussion in concentrick Spheres to great distances.
And in like manner, when a Ray of Light falls upon the Surface of any
pellucid Body, and is there refracted or reflected, may not Waves of
Vibrations, or Tremors, be thereby excited in the refracting or
reflecting Medium at the point of Incidence, and continue to arise
there, and to be propagated from thence as long as they continue to
arise and be propagated, when they are excited in the bottom of the Eye
by the Pressure or Motion of the Finger, or by the Light which comes
from the Coal of Fire in the Experiments above-mention'd? and are not
these Vibrations propagated from the point of Incidence to great
distances? And do they not overtake the Rays of Light, and by overtaking
them successively, do they not put them into the Fits of easy Reflexion
and easy Transmission described above? For if the Rays endeavour to
recede from the densest part of the Vibration, they may be alternately
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