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The following Lectures were delivered in the spring of 1843, before the Members of the PHARMACEUTICAL SOCIETY OF GREAT BRITAIN, and are now in course of publication in the Pharmaceutical Journal. The substance of them has formed, for some years past, a portion of the Annual Course on Chemistry, delivered in the MEDICAL SCHOOL of the London Hospital.

To the undermentioned eminent philosophers the author has been principally indebted for the information contained in the following pages :

Sir Isaac Newton.—Opticks; or, a Treatise of the Reflections, Refractions, Inflections, and Colours of Light.

Dr. Thomas Young.--A Course of Lectures on Natural Philosophy and the Mechanical Arts.

Sir D. Brewster.—Various papers in the Transactions of the Royal Societies of London and Edinburgh. Also two numbers on the Double Refraction and Polarization of Light, published under the superintendence of the Society for the Diffusion of Useful Knowledge. Likewise, a Treatise on Optics, in Lardner's Cyclopædia, and the article “ Optics” in the Encyclopædia Britannica, 7th edition.

Fresnel.- Elementary View of the Undulatory Theory of Light, in the Quarterly Journal of Science for 1827, 1828, 1829, translated and annotated by Dr. Thomas Young. Also various papers in the Annales de Chimie et de Physique. Likewise, Extrait du Bulletin de la Société Philomatique, Décembre, 1822, and Fevrier, 1823.

Sir J. Herschel. - Article 56 Light,” in the Encyclopædia Metropolitana. Also, Transactions of the Cambridge Philosophical Society, and Philosophical Transactions.

Biot.–Various papers in the Mémoires de l'Academie Royale des Sciences, and in the Annales de Chimie et de Physique.

Airy.- Mathematical Tracts. 2d edit. 1831. Also, Transactions of the Cambridge Philosophical Society.

Pouillet.-Elémens de Physique Expérimentale et de Météorologie, 2 vols. 1827.

Peclet.—Traité Elémentaire de Physique. 2me. ed. 2 vols. 1830.

Quetelet. Notes to the French Translation of Herschel's Article on Light. Also, Positions de Physique. 1834.

Lloyd, Rev. H.—Report on the Progress and Present State of Physical Optics, in the Report of the Fourth Meeting of the British Association. 1835. Also, Lectures on the Wave Theory of Light. 1841.

Powell, Rev. Professor.-Elementary Treatise on Experimental and Mathematical Optics. 1833. Also, a General and Elementary View of the Undulatory Theory, as applied to the Dispersion of Light. 1841. Likewise, various papers in the Philosophical Magazine.

Rose, Gustav. — Elemente der Krystallographie. 2te. Aufl. 1838. (A French translation of the 1st edition of this work).

Dove.-On the Circular Polarization of Light: translated in Taylor's Scientific Memoirs, vol. i.

Soubeiran.- Journal de Pharmacie. 1842.
Ventzke.-Annals of Chemistry. December, 1842.

The author takes this opportunity of offering his warmest thanks to his friend, Mr. Woodward, for his valuable assistance and advice on many occasions, in the performance of experiments on Polarized Light; as well as for the loan of various pieces of apparatus, contrived and adapted by Mr. Woodward, for the public illustration of the phenomena of Polarized Light.

To Mr. Darker, optician and manufacturer of polarizing apparatus, of Paradise Street, Lambeth, the thanks of the author are also justly due, for his disinterested zeal, skill, and attention in promoting the objects of the author in the preparation of the present course of Lectures.

J. P. 47, FINSBURY SQUARE,

September, 1843.

TABLE OF CONTENTS.

PAGE.

1

.........

LECTURE I. Introductory Remarks 1. GENERAL STATEMENT OF THE PHYSICAL PROPERTIES OF LIGHT.

1. Propagation. 2. Intensity, Photometry, Wheatstone's Photometer. 3. Transparency and Opacity. 4. Reflection. 5. Refraction. 6. Dispersion, the spectrum, primitive and compound colours, complementary tints, formation of white light, possible existence of a second spectrum, achromatism, Fraunhofer's lines. 7. Diffraction. 8. Colours of thin plates, of films, and of grooved surfaces, Newton's Fits, Nobili's Metallo- Chromes, Reade's Iriscope. 9. Double Refraction. 10. Polarization, methods of effecting it, by reflection, by single refraction, by double refraction, by the tourmaline

.3-20 2. WAVE HYPOTHESIS.—Light a property or motion, not a matter.

Ether, its existence assumed, its supposed resistance to the motions of the planets, retardation of Encke's comet. Ethereal Molecules. Waves, lengths for different colours ; comparative range of sensibility of the eye and ear. Vibrations, rectilinear, circular, elliptical. Powell's machine. Doctrine of transversal vibrations. Partially polarized light. Interferences of Light, Young's experiments ; his sliders, circular and elliptical waves how formed. Wheatstone's illustrative apparatus

20-33

..........

LECTURE II.

3. COLOURED POLARIZATION.Polariscope ; polarizer, depolarizer, and

analyzer. Colours of thin plates by polarized lights. Theory of their production. Selenite, description of, its optical properties, devices of

.34-41 Double refraction, test of, its cause. Effect of compression, and unequal

heating or cooling in producing double refraction, chromatic dynamometer, chromatic thermometer. Properties of unannealed glass. Practical application of the preceding statements. Argument for the vegetable origin of the Diamond. Doubly refractive power of starch grains and other organic substances ..

.41-50

LECTURE III.
Crystals, their doubly refractive power ; uniaxial and biaxial crystals ;

positive and negative axes. Forms of crystals ; crystallographical axes, classification of crystalline forms. Expansibility of crystals ; Mitscherlich's experiments. Atoms of crystals ; opinions as to their shape, probability that the atoms are susceptible of alteration of form. Molecular forces ; elasticity of crystals, Savart's experiments thereon. General conclusions

.50—64

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