Zoonomia, Vol. I | Page 9

the organ of touch into animal
action, which constitutes the perception of hardness and of figure; for
in some minutes the perception ceases, though the mechanical pressure
of the object remains.
3. Make with ink on white paper a very black spot about half an inch in
diameter, with a tail about an inch in length, so as to resemble a tadpole,
as in Plate II.; look steadfastly for a minute on the center of this spot,
and, on moving the eye a little, the figure of the tadpole will be seen on
the white part of the paper; which figure of the tadpole will appear

more luminous than the other part of the white paper; which can only
be explained by supposing that a part of the retina, on which the
tadpole was delineated, to have become more sensible to light than the
other parts of it, which were exposed to the white paper; and not from
any idea of mechanical impression or chemical combination of light
with the retina.
4. When any one turns round rapidly, till he becomes dizzy, and falls
upon the ground, the spectra of the ambient objects continue to present
themselves in rotation, and he seems to behold the objects still in
motion. Now if these spectra were impressions on a passive organ, they
either must continue as they were received last, or not continue at all.
5. Place a piece of red silk about an inch in diameter on a sheet of white
paper in a strong light, as in Plate I; look steadily upon it from the
distance of about half a yard for a minute; then closing your eye-lids,
cover them with your hands and handkerchief, and a green spectrum
will be seen in your eyes resembling in form the piece of red silk. After
some seconds of time the spectrum will disappear, and in a few more
seconds will reappear; and thus alternately three or four times, if the
experiment be well made, till at length it vanishes entirely.
[Illustration: Plate III.]
6. Place a circular piece of white paper, about four inches in diameter,
in the sunshine, cover the center of this with a circular piece of black
silk, about three inches in diameter; and the center of the black silk
with a circle of pink silk, about two inches in diameter; and the center
of the pink silk with a circle of yellow silk, about one inch in diameter;
and the center of this with a circle of blue silk, about half an inch in
diameter; make a small spot with ink in the center of the blue silk, as in
Plate III.; look steadily for a minute on this central spot, and then
closing your eyes, and applying your hand at about an inch distance
before them, so as to prevent too much or too little light from passing
through the eye-lids, and you will see the most beautiful circles of
colours that imagination can conceive; which are most resembled by
the colours occasioned by pouring a drop or two of oil on a still lake in
a bright day. But these circular irises of colours are not only different

from the colours of the silks above mentioned, but are at the same time
perpetually changing as long as they exist.
From all these experiments it appears, that these spectra in the eye are
not owing to the mechanical impulse of light impressed on the retina;
nor to its chemical combination with that organ; nor to the absorption
and emission of light, as is supposed, perhaps erroneously, to take place
in calcined shells and other phosphorescent bodies, after having been
exposed to the light: for in all these cases the spectra in the eye should
either remain of the same colour, or gradually decay, when the object is
withdrawn; and neither their evanescence during the presence of their
object, as in the second experiment, nor their change from dark to
luminous, as in the third experiment, nor their rotation, as in the fourth
experiment, nor the alternate presence and evanescence of them, as in
the fifth experiment, nor the perpetual change of colours of them, as in
the last experiment, could exist.
IV. The subsequent articles shew, that these animal motions or
configurations of our organs of sense constitute our ideas.
1. If any one in the dark presses the ball of his eye, by applying his
finger to the external corner of it, a luminous appearance is observed;
and by a smart stroke on the eye great slashes of fire are perceived.
(Newton's Optics.) So that when the arteries, that are near the auditory
nerve, make stronger pulsations than usual, as in some fevers, an
undulating sound is excited in the ears. Hence it is not the presence