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Opticks Isaac Newton Public domain text from Project Gutenberg. OPTICKS: OR, A TREATISE OF THE _Reflections_, _Refractions_, _Inflections_ and _Colours_ OF LIGHT. _The_ FOURTH EDITION, _corrected_. By Sir _ISAAC NEWTON_, Knt. LONDON: Printed for WILLIAM INNYS at the West-End of St. _Paul's_. MDCCXXX. TITLE PAGE OF THE 1730 EDITION SIR ISAAC NEWTON'S ADVERTISEMENTS 1 Advertisement I _Part of the ensuing Discourse about Light was written at the Desire of some Gentlemen of the_ Royal-Society, _in the Year 1675, and then sent to their Secretary, and read at their Meetings, and the rest was added about twelve Years after to complete the Theory; except the third Book, and the last Proposition of the Second, which were since put together out of scatter'd Papers. To avoid being engaged in Disputes about these Matters, I have hitherto delayed the printing, and should still have delayed it, had not the Importunity of Friends prevailed upon me. If any other Papers writ on this Subject are got out of my Hands they are imperfect, and were perhaps written before I had tried all the Experiments here set down, and fully satisfied my self about the Laws of Refractions and Composition of Colours. I have here publish'd what I think proper to come abroad, wishing that it may not be translated into another Language without my Consent._ _The Crowns of Colours, which sometimes appear about the Sun and Moon, I have endeavoured to give an Account of; but for want of sufficient Observations leave that Matter to be farther examined. The Subject of the Third Book I have also left imperfect, not having tried all the Experiments which I intended when I was about these Matters, nor repeated some of those which I did try, until I had satisfied my self about all their Circumstances. To communicate wha…

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Page 183 of 233, printed 183

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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 -------------------------------------------+-----------+-------- 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, | | 183

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