concourse of their edges; and therefore the Light which falls upon the
Paper where those dark Lines meet passes between the Knives where the
edges are distant above the 160th part of an Inch.
For at another time, when the two Knives were distant eight Feet and
five Inches from the little hole in the Window, made with a small Pin as
above, the Light which fell upon the Paper where the aforesaid dark
lines met, passed between the Knives, where the distance between their
edges was as in the following Table, when the distance of the Paper from
the Knives was also as follows.
-----------------------------+------------------------------
| Distances between the edges
Distances of the Paper | of the Knives in millesimal
from the Knives in Inches. | parts of an Inch.
-----------------------------+------------------------------
1-1/2. | 0'012
3-1/3. | 0'020
8-3/5. | 0'034
32. | 0'057
96. | 0'081
131. | 0'087
_____________________________|______________________________
And hence I gather, that the Light which makes the Fringes upon the
Paper is not the same Light at all distances of the Paper from the
Knives, but when the Paper is held near the Knives, the Fringes are made
by Light which passes by the edges of the Knives at a less distance, and
is more bent than when the Paper is held at a greater distance from the
Knives.
[Illustration: FIG. 3.]
_Obs._ 10. When the Fringes of the Shadows of the Knives fell
perpendicularly upon a Paper at a great distance from the Knives, they
were in the form of Hyperbola's, and their Dimensions were as follows.
Let CA, CB [in _Fig._ 3.] represent Lines drawn upon the Paper parallel
to the edges of the Knives, and between which all the Light would fall,
if it passed between the edges of the Knives without inflexion; DE a
Right Line drawn through C making the Angles ACD, BCE, equal to one
189