, or half an Inch, and in all its progress from that
direct Light decreased gradually till it became insensible. The whole
length of either of these streams measured upon the paper at the
distance of three Feet from the Knife was about six or eight Inches; so
that it subtended an Angle at the edge of the Knife of about 10 or 12,
or at most 14 Degrees. Yet sometimes I thought I saw it shoot three or
four Degrees farther, but with a Light so very faint that I could scarce
perceive it, and suspected it might (in some measure at least) arise
from some other cause than the two streams did. For placing my Eye in
that Light beyond the end of that stream which was behind the Knife, and
looking towards the Knife, I could see a line of Light upon its edge,
and that not only when my Eye was in the line of the Streams, but also
when it was without that line either towards the point of the Knife, or
towards the handle. This line of Light appear'd contiguous to the edge
of the Knife, and was narrower than the Light of the innermost Fringe,
and narrowest when my Eye was farthest from the direct Light, and
therefore seem'd to pass between the Light of that Fringe and the edge
of the Knife, and that which passed nearest the edge to be most bent,
though not all of it.

_Obs._ 6. I placed another Knife by this, so that their edges might be
parallel, and look towards one another, and that the beam of Light might
fall upon both the Knives, and some part of it pass between their edges.
And when the distance of their edges was about the 400th part of an
Inch, the stream parted in the middle, and left a Shadow between the two
parts. This Shadow was so black and dark that all the Light which passed
between the Knives seem'd to be bent, and turn'd aside to the one hand
or to the other. And as the Knives still approach'd one another the
Shadow grew broader, and the streams shorter at their inward ends which
were next the Shadow, until upon the contact of the Knives the whole
Light vanish'd, leaving its place to the Shadow.

And hence I gather that the Light which is least bent, and goes to the
inward ends of the streams, passes by the edges of the Knives at the
greatest distance, and this distance when the Shadow begins to appear
between the streams, is about the 800th part of an Inch. And the Light
which passes by the edges of the Knives at distances still less and
less, is more and more bent, and goes to those parts of the streams
which are fa