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.
| At the Distance of | half a Foot | Nine Feet |
|---|---|---|
| The breadth of the Shadow | 1/54 | 1/9 |
| The breadth between the Middles of the brightest Light of the innermost Fringes on either side the Shadow | 1/38 or 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 brightest Light of the outmost Fringes on either side the Shadow | 1/18 or 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 |
| The distance between the Middles of the brightest Light of the second and third Fringes | 1/170 | 1/31 |
| The breadth of the luminous Part (green, white, yellow, and red) of the first Fringe | 1/170 | 1/32 |
| The breadth of the darker Space between the first and second Fringes | 1/240 | 1/45 |
| The breadth of the luminous Part of the second Fringe | 1/290 | 1/55 |
| The breadth of the darker Space between the second and third Fringes | 1/340 | 1/63 |
These Measures I took by letting the Shadow of the Hair, at half a Foot distance, fall so obliquely on the Scale, as to appear twelve times broader than when it fell perpendicularly on it at the same distance, and setting down in this Table the twelfth part of the Measures I then took.