ons,
and indeed of some more then I was willing there should be; which was
occasioned by my first Intentions to print a much greater number then I
have since found time to compleat. Of such therefore as I had, I selected
only some few of every Head, which for some particulars seem'd most
observable, rejecting the rest as superfluous to the present Design.

What each of the delineated Subjects are, the following descriptions
annext to each will inform, of which I shall here, only once for all, add,
That in divers of them the Gravers have pretty well follow'd my directions
and draughts; and that in making of them, I indeavoured (as far as I was
able) first to discover the true appearance, and next to make a plain
representation of it. This I mention the rather, because of these kind of
Objects there is much more difficulty to discover the true shape, then of
those visible to the naked eye, the same Object seeming quite differing, in
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
Ob