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Hooke, Robert, 1635-1703 / Micrographia: or some physiological descriptions of minute bodies made by magnifying glasses : with observations and inquiries thereupon
(MDCLXVII [1667])

Observ. XXXIX. Of the eyes and head of a grey drone-fly, and of several other creatures,   pp. 175-180

Page 179

             1 I CROG R AP HIA                                       I7A
lateral points of any Obje& as to colle& them again,and unite them
in a diftin& point,and that onely thofe Rays which come from fome point
that lies in the Axi of the Figure produc'd > are fo accurately re-
fraaed to one and the fame point again, and that the lateral Rays,thefur
ther they are remov'd, the more imperfe& is their refrated confluence
It follows therefore, that onely the Picture of thofe parts of the external
objeds that lie in, or neer, the Axis of each Hemijfphere, 'are dikernably
painted or made on the Retina of each Hem4irhere, and that therefore
each of them can diftindilyfenfate or fee onely thofe parts which are very
neer perpendicularly cppos'd to it, or lie in or neer its optick Axii.
Now, though there may be by each of thefe eye-pearlsva reprefentation
to the Animal ofa whole HCovfiphere in the fame. manner as in a man's eye
there is a piaure or fentation in the Retina of all the objefs lying almoft
in an Hemipjhcre 5 yet, as in a man's eye alfo, there are but fome very
few points which fiyng in, or neer, the optick Axis are diftintly dif-
cern'd: So there may be multitudes of Pi~tures made of an Obje&t in
the feveral Pearls, and yet but one, or fome very few that are diftina;
The representation of any obje& that is made in any other Pearl, but
which is direaly,or very neer direflyoppos'd,being altogether confus'd
and unable to produce a dihin& vifion.-
  So that we fee, that though it has pleas'd the All-wife Creator,. to in-
due thiscreature with fuch multitudes of eyes, yet has he not indued it
with the faculty of feeing more then another creatures for whereas this
cannot move his headat leaft can move itvery little,without moving his
whole body, blocular creatures can in an inftant (or the twinkling of an
eye, which, being very quick, is vulgarly ufed in the fame fignification)
move their eyes fo as t'o dire&t the optick AxAi to any point i nor is
probable, that they are able to fee attentively at one time more then one
Phy fical point - for though there be i diftin~Wmage made in every eye,
yet tis very likely,that the obferving faculty is only imploy'd about fbome
one obje& for which they have moft concern.
  Now, as we accurately diflinguilh the fite or pofition of an Obje&k
by the motion of the Mufcles of the eye requifite to put the optick Line
in a dire&i pofition,and confufedly by the pofition ofthe imperfe&
of the object at the bottom of the eye; fo are thefe crx Jiaceow creatures
able to judge confufedly of the pofition of obje&s by the Piaure or im-
preflion made at the bottom of the oppofite Pearl, and diflinaly by the
removal of the attentive or obferving faculty, from one Pearl toaanotherb
but what this faculty islas it requires another place, fo a much deeper fpe'
culation. Now,becaufeit were impoflibleeven with this multitude ofeye-
ballsto fee any obje& diftindt(for as I hinted before,onely thofe parts
lay inor veryneer,the optick Lines could be fo)the Infinitely wife Creator
has not left the creature without a power of moving the head a little in
AerialcrufJaceow animalsand the very eyes alfo in cruftaceou Sea-animals;
fo that by thefe means they are inabled to dire& fome optick line or
againfi any obje&,and by that means they have the vifive faculty as com-
pleat as any Animal that can move its eyes.
                                   E; b a                  Diftances

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