breadth of the bright Light or
luminous part of the first Fringe. And this breadth was to the breadth
of the bright Light of the second Fringe as seven to four, and to the
dark Interval of the first and second Fringe as three to two, and to
the like dark Interval between the second and third as two to one. For
the breadths of the Fringes seem'd to be in the progression of the
Numbers 1, sqrt(1/3), sqrt(1/5), and their Intervals to be in the
same progression with them; that is, the Fringes and their Intervals
together to be in the continual progression of the Numbers 1,
sqrt(1/2), sqrt(1/3), sqrt(1/4), sqrt(1/5), or thereabouts. And
these Proportions held the same very nearly at all distances from the
Hair; the dark Intervals of the Fringes being as broad in proportion to
the breadth of the Fringes at their first appearance as afterwards at
great distances from the Hair, though not so dark and distinct.

_Obs._ 5. The Sun shining into my darken'd Chamber through a hole a
quarter of an Inch broad, I placed at the distance of two or three Feet
from the Hole a Sheet of Pasteboard, which was black'd all over on both
sides, and in the middle of it had a hole about three quarters of an
Inch square for the Light to pass through. And behind the hole I
fasten'd to the Pasteboard with Pitch the blade of a sharp Knife, to
intercept some part of the Light which passed through the hole. The
Planes of the Pasteboard and blade of the Knife were parallel to one
another, and perpendicular to the Rays. And when they were so placed
that none of the Sun's Light fell on the Pasteboard, but all of it
passed through the hole to the Knife, and there part of it fell upon the
blade of the Knife, and part of it passed by its edge; I let this part
of the Light which passed by, fall on a white Paper two or three Feet
beyond the Knife, and there saw two streams of faint Light shoot out
both ways from the beam of Light into the shadow, like the Tails of
Comets. But because the Sun's direct Light by its brightness upon the
Paper obscured these faint streams, so that I could scarce see them, I
made a little hole in the midst of the Paper for that Light to pass
through and fall on a black Cloth behind it; and then I saw the two
streams plainly. They were like one another, and pretty nearly equal in
length, and breadth, and quantity of Light. Their Light at that end next
the Sun's direct Light was pretty strong for the space of about a
quarter of an Inch