one position to the Light, from what it really is, and may be discover'd in
another. And therefore I never began to make any draught before by many
examinations in several lights, and in several positions to those lights, I
had discover'd the true form. For it is exceeding difficult in some
Objects, to distinguish between a _prominency_ and a _depression_, between
a _shadow_ and a _black stain_, or a _reflection_ and a _whiteness in the
colour_. Besides, the transparency of most Objects renders them yet much
more difficult then if they were _opacous_. The Eyes of a Fly in one kind
of light appear almost like a Lattice, drill'd through with abundance of
small holes; which probably may be the Reason, why the Ingenious _Dr.
Power_ seems to suppose them such. In the Sunshine they look like a Surface
cover'd with golden Nails; in another posture, like a Surface cover'd with
Pyramids; in another with Cones; and in other postures of quite other
shapes; but that which exhibits the best, is the Light collected on the
Object, by those means I have already describ'd.

And this was undertaken in prosecution of the Design which the _ROYAL
SOCIETY_ has propos'd to it self. For the Members of the Assembly having
before their eys so many _fatal_ Instances of the errors and falshoods, in
which the greatest part of mankind has so long wandred, because they rely'd
upon the strength of humane Reason alone, have begun anew to correct all
_Hypotheses_ by sense, as Seamen do their _dead Reckonings_ by _Coelestial
Observations_; and to this purpose it has been their principal indeavour to
_enlarge & strengthen_ the _Senses_ by _Medicine_, and by such _outward
Instruments_ as are proper for their particular works. By this means they
find some reason to suspect, that those effects of Bodies, which have been
commonly attributed to _Qualities_, and those confess'd to be _occult_, are
perform'd by the small _Machines_ of Nature, which are not to be discern'd
without these helps, seeming the meer products of _Motion_, _Figure_, and
_Magnitude_; and that the _Natural Textures_, which some call the _Plastick