Opticks

Isaac Newton · 1675 (Books I-II); ~1687 (Books II-III completion) [with later assembly before 1704]; opening notes say third Book + last Proposition of Second added about twelve years after 1675; fourth-edition corrections copied from Third Edition corrected by author and left before his death (1710s) primary

passage 48 of 188 · Book might be made to converge and meet again at the distance of six > Part of the Diameter of the Aperture of the Glass. And if you add the brighter half of the red, (that half which is next the orange) and the brighter half of the green, (that half which is next the yellow) about three fifth Parts of the Light of these two Colours will fall within the same Circle, and two fifth Parts will fall without it round about; and that which falls without will be spread through almost as much more space as that which falls within, and so in the gross be almost three times rarer. Of the other half of the red and green, (that is of the deep dark red and willow green) about one quarter will fall within this (6/18)

in brief

He explains the ultimate limit on telescope performance: atmospheric turbulence blurs starlight, and while long telescopes can brighten and enlarge images, only very calm air (e.g., mountain tops) can reduce confusion.

and the Eye-glass. If it be desired that the Instrument bear a larger aperture, that may be also done by composing the Speculum of two Glasses with Water between them.

If the Theory of making Telescopes could at length be fully brought into Practice, yet there would be certain Bounds beyond which Telescopes could not perform. For the Air through which we look upon the Stars, is in a perpetual Tremor; as may be seen by the tremulous Motion of Shadows cast from high Towers, and by the twinkling of the fix'd Stars. But these Stars do not twinkle when viewed through Telescopes which have large apertures. For the Rays of Light which pass through divers parts of the aperture, tremble each of them apart, and by means of their various and sometimes contrary Tremors, fall at one and the same time upon different points in the bottom of the Eye, and their trembling Motions are too quick and confused to be perceived severally. And all these illuminated Points constitute one broad lucid Point, composed of those many trembling Points confusedly and insensibly mixed with one another by very short and swift Tremors, and thereby cause the Star to appear broader than it is, and without any trembling of the whole. Long Telescopes may cause Objects to appear brighter and larger than short ones can do, but they cannot be so formed as to take away that confusion of the Rays which arises from the Tremors of the Atmosphere. The only Remedy is a most serene and quiet Air, such as may perhaps be found on the tops of the highest Mountains above the grosser Clouds.

FOOTNOTES:

[C] See our Author's Lectiones Opticæ § 10. Sect. II. § 29. and Sect. III. Prop. 25.

[D] See our Author's Lectiones Opticæ, Part. I. Sect. 1. §5.

[E] This is very fully treated of in our Author's Lect. Optic. Part I. Sect. II.

[F] See our Author's Lect. Optic. Part I. Sect. II. § 29.

[G] This is demonstrated in our Author's Lect. Optic. Part I. Sect. IV. Prop. 37.

[H] How to do this, is shewn in our Author's Lect. Optic. Part I. Sect. IV. Prop. 31.

THE FIRST BOOK OF OPTICKS

PART II.

PROP. I. THEOR. I.

The Phænomena of Colours in refracted or reflected Light are not caused by new Modifications of the Light variously impress'd, according to the various Terminations of the Light and Shadow.

The PROOF by Experiments.

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topics: experiment, observation, and evidence · weather, storms, and the seasons

Opticks · Isaac Newton · 1675–1687