The Life of Sir Isaac Newton

ton determines the Law of their Production-His Theory of Fit

. His earliest researches on this subject were communicated, in his Discourse on Light and Colours, to the Royal Society, on the 9th December, 1675, and were read at subsequent meetings of that body. This discourse contained fuller details

mena, as exhibited in the coloured rings upon soap-bubbles, and between plates of glass pressed together. He recognised that the colour depended upon some certain thickne

which the colour varied with the thickness of the film. Newton surmounted this difficulty by laying a double convex lens, the radius of curvature of each side of which was fifty feet, upon the flat surface of a plano-convex object-glass, and in this way he obtained a plate of air or of space varying from the thinnest possible edge at the centre of the object-glass where it touched the plane surface, to a considerable thickness at the circumference of the lens. Whe

is wholly transmitted, and, consequently, to an eye above E, there will appear at E a black spot. At a, where the plate of air is thicker, the red light ra is reflected in the direction aa′, and as the air has the same thickness in a circle round the point E, the eye above E, at a, will see next the black spot E a ring of red light. At m,77 where the thickness o

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e very same phenomenon was observed; with this difference only, that the rings were largest in red

before, but they will have a bright spot in their centre at E, and the luminous rings will now correspond with th

once. Had the rings in each colour been all of the same diameter they would all have formed brilliant white rings, separated by dark intervals; but, as they have all

blue, white, yel

blue, green, yel

blue, green, yello

-green, green, ye

Greenish-

Greenish-

nce of the thin plate is water, as in the case of the soap-bubble, which produces beautiful colours according to its different degrees of thinness, the thicknesses at which the most luminous parts of the rings appear are produced at 1/1·336 of the th

position to be reflected, it will yield more readily to the reflecting force of the surface; and, on the contrary, if it reaches the same surface while in a fit of easy transmission, or in a disposition to be transmitted, it will yield with more difficulty to the reflecting force. Sir Isaac has not ventured to inquire into the cause of this property; but we may form a very intelligible idea of it by supposing, that the particles of light have two attractive and two repulsive poles at the extremities of two axes at right angles to each other, and that th

e at E. When the plate becomes thicker towards a, so that its thickness exceeds half of F, the light will not reach the surface CE till it has come under its fit of reflection, and consequently at a the light will be all reflected, and none transmitted. As the thickness increases towards m, the light will have come under its fit of transmission, and so on, the light being reflected at a, l, and transmitted at E, m. This will perhaps be still more easily understood from fig. 9, where we may suppose AEC to be a thin wedge of glass or any other transparent body. When light is incident on the first surface AE, all the particles of it that are in a fit of easy reflection will be reflected, and all those in a fit of easy transmission will be transmitted. As the fits of transmission all commence at AE, let the first fit of transmission end when the particles of light have reached ab, and the second when they have reache

own glass, it has numerous inequalities, then the alternate fringes of light and darkness will vary with the t

it is white, then the differently coloured fringes will form by their superposition a sy

by means of the theory of fits; but it would lead us beyond the limits of a popular work like this to enter into any details of his observations, or to g