Of the Forces which produce the Reflection of Light at the Sur-

faces of Bodies

• DIOPTRICS.

General Laws of Simple Refraction

Exact Determination of the Ratio of Refraction in Solid Sub-

stances

7

11

16

21

23

3333

37

40

46

Determination of the Ratio of Refraction in Liquids

Determination of the Ratio of Refraction in Aeriform Substances 42

Of Spherical Lenses

Determination of the Images produced by Diverging Lenses.

Use of these Lenses in correcting shortsightedness

Method of determining the Images produced by Converging

Lenses. Use of these Lenses in correcting the defective

Vision of longsighted Persons

52

56

60

65

93

12

Passage of Light through several Contiguous Bodies possessing

the Power of Double Refraction

Construction of Double Image Micrometers

Of the Dispersion of Light produced by Refraction

Recomposition of Colours

137

140

143

164

168

Compound Colours produced by the Mixture of Simple ones

Influence of the Unequal Refrangibility of Rays of Light upon

Vision through Refracting Surfaces

Of the Dispersion which accompanies Extraordinary Refraction,

and the Separation of the Axes of Double Refraction with

respect to the different Simple Rays

184

Method of M. Arago for determining the Magnifying Power of

Megascope

Solar Microscope

Camera Lucida

Organ of Vision

Reflections, Refractions, and Colours of thin Transparent Bodies 221

Colours produced by thin Lamina

Fits of easy Reflection and easy Transmission

Application of the preceding Theory to the Reflection of Rays

of Light which have traversed thick Media

281

287

292

Explanation of the proper and permanent Colours of Bodies

Return of Rays reflected interiorly at the second Surface of thick

transparent Media

Explanation of Coloured Rings and Fits upon the Hypothesis

of the Undulations of Light. Principle of Interferences 293

Diffraction or Inflection of Light

NOTES.

I. Of the Spherometer

II. Polarisation of Light

313

314

III. The Relations of Light and Heat or Caloric

IV. Measure of the Intensities of Light

VI. New Optical Experiments and the Improvement of Glass 335

VII. On the Magnetising Power of the more refrangible Rays

of Light

VII. Of the Colours of Striated Surfaces

345

348

Table of the Refractive and Dispersive Powers of different sub-

stances

350

AN

ELEMENTARY TREATISE

ON

OPTICS.

General Remarks.

1. WHEN the sun first appears above the horizon and presents itself suddenly to our view, we feel persuaded that there must be some mode of communication between this luminary and ourselves, which informs us of its existence without the necessity of our coming in contact with it. This mode of communication, which thus takes place at a distance, and through the medium of the sight, constitutes what is called light. Bodies, which are capable of exciting it directly, and of thus making themselves known to us, are called self-luminous, as the sun and stars. It would seem, indeed, that all material substances become self-luminous when their temperature is sufficiently raised, and they lose this property by being deprived of their heat. If they receive light, however, from a luminous body, after they have ceased to be self-luminous, they are still capable of sending to us the light thus received, as if it were their own, and in this case they become visible by reflection. In this way we perceive the objects about us while the sun is above the horizon, and all becomes obscure and invisible when this light is withdrawn.

In all cases, when an object transmits to us a sensation of its existence by means of light, this transmission takes place in a right line; for if we place fine threads of silk or metal parallel to each other and in the same plane, a luminous point situated at some distance beyond the threads in the same plane will be eclipsed by them; but if we move it a little out of the direction of this plane, it will become visible. Moreover, if we take two metallic plates perfectly plane and bring them by degrees to