Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

Of certain Singular Appearances occasioned by Double Refrac-

tion . . . . . . . . . 137

Of Double Refraction in Compressed Glass . . . 140

ANALYSIS OF LIGHT.

Of the Dispersion of Light produced by Refraction. . 143

Recomposition of Colours . . . . . . 159

Compound Colours produced by the Mixture of Simple ones 164

Influence of the Unequal Refrangibility of Rays of Light upon

Vision through Refracting Surfaces . . . 168

Rainbow . . . . . . . . . 171

Achromatic Combinations . ... . . . 176

Of the Dispersion which accompanies Extraordinary Refraction,

and the Separation of the Axes of Double Refraction with

respect to the different Simple Rays . . . . 184

Dioptric Instruments consisting of several Glasses . . 186

Compound Microscope . . . . . . . 187

Amplifying Glass and Achromatic Eye-Glasses . . 195

Dioptric or Refracting Telescope . . . . . 198

Instruments which consist of a Combination of Mirrors and

Spherical Lenses.

. . . 201

Method of M. Arago for determining the Magnifying Power of

Optical Instruments

Instruments employed in Optical Experiments

206

Camera Obscura . . . . . . . . . ib.

Megascope . . . . . . . . 207

Solar Microscope . . . . . . . . 208

Camera Lucida . . . . . . . . 209

Organ of Vision . . . . . . . . ib.

Reflections, Refractions, and Colours of thin Transparent Bodies 221

Colours produced by thin Lamina . . . . 223

Fits of easy Reflection and easy Transmission . . . 265

Application of the preceding Theory to the Reflection of Rays

of Light which have traversed thick Media . . 281

Explanation of the proper and permanent Colours of Bodies 287

Return of Rays reflected interiorly at the second Surface of thick

transparent Media . . . . . . . 292

Explanation of Coloured Rings and Fits upon the Hypothesis

of the Undulations of Light. Principle of Interferences 293

Diffraction or Inflection of Light.

302

.

.

.

204

[merged small][graphic][subsumed]

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 toOpt.

1

« ΠροηγούμενηΣυνέχεια »