AB. And let all the Light
between the Rays ENI and FBM pass directly through the parallel Planes
of the Glass, and fall upon the Paper between I and M, and all the Light
between the Rays GO and HD be refracted by the oblique Plane of the
Diamond-cut BD, and fall upon the Paper between K and L; and the Light
which passes directly through the parallel Planes of the Glass, and
falls upon the Paper between I and M, will be border'd with three or
more Fringes at M.

[Illustration: FIG. 1.]

[Illustration: FIG. 2.]

So by looking on the Sun through a Feather or black Ribband held close
to the Eye, several Rain-bows will appear; the Shadows which the Fibres
or Threds cast on the _Tunica Retina_, being border'd with the like
Fringes of Colours.

_Obs._ 3. When the Hair was twelve Feet distant from this Hole, and its
Shadow fell obliquely upon a flat white Scale of Inches and Parts of an
Inch placed half a Foot beyond it, and also when the Shadow fell
perpendicularly upon the same Scale placed nine Feet beyond it; I
measured the breadth of the Shadow and Fringes as accurately as I could,
and found them in Parts of an Inch as follows.

-------------------------------------------+-----------+--------
| half a | Nine
At the Distance of | Foot | Feet
-------------------------------------------+-----------+--------
The breadth of the Shadow | 1/54 | 1/9
-------------------------------------------+-----------+--------
The breadth between the Middles of the | 1/38 |
brightest Light of the innermost Fringes | or |
on either side the Shadow | 1/39 | 7/50
-------------------------------------------+-----------+--------
The breadth between the Middles of the | |
brightest Light of the middlemost Fringes| |
on either side the Shadow | 1/23-1/2 | 4/17
-------------------------------------------+-----------+--------
The breadth between the Middles of the | 1/18 |
brightest Light of the outmost Fringes | or |
on either side the Shadow | 1/18-1/2 | 3/10
-------------------------------------------+-----------+--------
The distance between the Middles of the | |
brightest Light of the first and second | |
Fringes | 1/120 | 1/21
------------------------