SECTION XXVI.

Influence of Temperature on Vegetation — Vegetation varies with the Lati-

tude and Height above the Sea - Geographical Distribution of Land

Plants - Distribution of Marine Plants – Corallines, Shell-fish, Reptiles,

Insects, Birds, and Quadrupeds — Varieties of Mankind, yet identity of

Species

Page 248

SECTION XXVII.

-

-

Terrestrial Heat — Radiation — Transmission — Melloni's experiments -

Heat in Solar Spectrum Polarization of Heat - Nature of Heat

Absorptions — Dew — Rain Combustion — Expansion - Compensa-

tion Pendulum - Transmission through Crystals Propagation

Dynamic Theory of Heat — Mechanical equivalent of Heat Latent

Heat is the Force of Expansion — Steam - · Work performed by Heat —

Conservation of Force — Mechanical Power in the Tides Dynamical

Power of Light — Analogy between Light, Heat, and Sound 257

SECTION XXVIII.

Common or Static Electricity, or Electricity of Tension - A Dual Power

Methods of exciting it Attraction and Repulsion — Conduction

Electrics and Non-electrics - Induction - Dielectrics — Tension — Law

of the Electric Force- Distribution - Laws of Distribution Heat of

Electricity — Electrical Light and its Spectrum — Velocity -- Atmos-

pheric Electricity

Its cause

- Electric Clouds — Violent effects of

Lightning — Back Stroke - Electric Glow - Phosphorescence 282

SECTION XXIX.

-

Voltaic Electricity - The Voltaic Battery - Intensity - Quantity -Static

Electricity, and Electricity in Motion — Luminous Effects Mr. Grove

on the Electric Arc and Light — Decomposition of Water - Formation

of Crystals by Voltaic Electricity - Photo-galvanic Engraving — Con-

duction - Heat of Voltaic Electricity Electric Fish

297

SECTION XXX.

Discovery of Electro-magnetism Deflection of the Magnetic Needle by a

Current of Electricity - Direction of the Force Rotatory Motion by

Electricity Rotation of a Wire and a Magnet - Rotation of a Magnet

about its Axis — Of Mercury and Water - Electro-Magnetic Cylinder

or Helix — Suspension of a Needle in a Helix — Electro-Magnetic Induc-

tion - Temporary Magnets --The Galvanometer

312

SECTION XXXI.

Electro-Dynamics Reciprocal Action of Electric Currents — Identity of

Electro-Dynamic Cylinders and Magnets — Differences between the Action

of Voltaic Electricity and Electricity of Tension — Effects of a Voltaic

Current — Ampère's Theory – Dr. Faraday's Experiment of Electrifying

and Magnetising a Ray of Light'.

Page 316

SECTION XXXII.

Magneto-Electricity - Volta-Electric Induction - Magneto-Electric Induc-

tion — Identity in the Action of Electricity and Magnetism — Descrip-

tion of a Magneto-Electric Apparatus and its Effects - Identity of

Magnetism and Electricity — The Submarine Telegraph

322

SECTION XXXIII.

Electricity produced by Rotation - Direction of the Currents — Electricity

from the Rotation of a Magnet — M. Arago's Experiment explained

Rotation of a Plate of Iron between the Poles of a Magnet Relation of

Substances to Magnets of three Kinds Thermo-Electricity 330

SECTION XXXIV,

Magnetism a Dual Power - Antithetic Character of Paramagnetism and

Diamagnetism – The Earth Paramagnetic - Properties of Paramagnetic

Bodies Polarity — Induction · Lines of Magnetic Force - Currents

of Electricity induced by them Proved to be Closed Curves — Analogy

and Identity of Electricity and Magnetism · Terrestrial Magnetism

Mean Values of the Three Magnetic Elements — Their Variations in

Double Progression proved to consist of Two Superposed Variations

Discovery of the Periodicity of the Magnetic Storms The Decennial

Period of the Magnetic Elements the same with that of the Solar Spots

- Magnetism of the Atmosphere — Diamagnetism - Action of Electro-

Magnetism on Paramagnetic, Diamagnetic Bodies, and on Copper, very

different Proof of Diamagnetic Polarity and Induction - Magne-

crystallic Action - Effects of Compression, Heat, and Cleavage on Mag-

netic Bodies — Mutual Dependence of Light, Heat, Electricity, &c. &c.

- The Conservation of Force and the Permanency of Matter Primary

Laws of Nature - Definition of Gravity not according to that Law

Gravity only the Residual Force of a Universal Power - Magnetism of

the Ethereal Medium

335

SECTION XXXV.

Ethereal Medium - Comets - Do not disturb the Solar System — Their

Orbits and Disturbances M. Faye's Comet probably the same with

Lexel's Periods of other three known Acceleration in the mean

Motions of Encke's and Biela's Comets — The Shock of a Comet --- Dis-

turbing Action of the Earth and Planets on Encke's and Biela's Comets

Velocity of Comets - The Comet of 1264 — The great Comet of

1343 — Physical Constitution — Shine by borrowed Light Estima-

tion of their Number

358

SECTION XXXVI.

The Fixed Stars - Their Number · The Milky Way - Double Stars

Binary Systems Their Orbits and Periodic Times - Colours of the

Stars Stars that have vanished - Variable Stars - Variation in Sun's

Light - Parallax and Distances of the Fixed Stars - Masses of the Stars

- Comparative Light of the Stars - Proper Motions of the Stars

Apparent Motions of the Stars — Motion and Velocity of the Sun and

Solar System – The Nebulæ — Their Number — Catalogue of them -

Consist of Two Classes - Diffuse Nebulæ Definitely formed Nebulæ

- Globular Clusters — Splendour of Milky Way — Distribution of the

Nebulæ - The Magellanic Clouds -- Nebulæ round , Argûs — Consti-

tution of Nebulæ, and the Forces that maintain them Meteorites and

Shooting Stars

Page 384

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-

SECTION XXXVII.

Diffusion of Matter through Space — Gravitation — Its Velocity — Sim-

plicity of its Laws — Gravitation independent of the Magnitude and

Distances of the Bodies - Not impeded by the intervention of any

Substance — Its Intensity invariable — General Laws — Recapitulation

and Conclusion

424

THE

CONNECTION

OF

THE PHYSICAL SCIENCES.

INTRODUCTION.

SCIENCE, regarded as the pursuit of truth, must ever afford occupation of consummate interest, and subject of elevated meditation. The contemplation of the works of creation elevates the mind to the admiration of whatever is great and noble ; accomplishing the object of all study, which, in the eloquent language of Sir James Mackintosh, “ is to inspire the love of truth, of wisdom, of beauty—especially of goodness, the highest beautyand of that supreme and eternal Mind, which contains all truth and wisdom, all beauty and goodness. By the love or delightful contemplation and pursuit of these transcendent aims, for their own sake only, the mind of man is raised from low and perishable objects, and prepared for those high destinies which are appointed for all those who are capable of them.”

Astronomy affords the most extensive example of the connection of the physical sciences. In it are combined the sciences of number and quantity, of rest and motion. In it we perceive the operation of a force which is mixed up with everything that exists in the heavens or on earth ; which pervades every atom, rules the motions of animate and inanimate beings, and is as sensible in the descent of a rain-drop as in the falls of Niagara ; in the weight of the air, as in the periods of the moon, Gravitation not only binds satellites to their planet, and planets to the sun, but it connects sun with sun throughout the wide extent of creation, and is the cause of the disturbances, as well as of the order of nature; since every tremor it excites in any one planet

B

a

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is immediately transmitted to the farthest limits of the system, in oscillations which correspond in their periods with the cause producing them, like sympathetic notes in music, or vibrations from the deep tones of an organ.

The heavens afford the most sublime subject of study which can be derived from science. The magnitude and splendour of the objects, the inconceivable rapidity with which they move, and the enormous distances between them, impress the mind with some notion of the energy that maintains them in their motions, with a durability to which we can see no limit. Equally conspicuous is the goodness of the great First Cause, in having endowed man with faculties, by which he can not only appreciate the magnificence of His works, but trace, with precision, the operation of His laws, use the globe he inhabits as a base wherewith to measure the magnitude and distance of the sun and planets, and make the diameter (Note 1) of the earth's orbit the first step of a scale by which he may ascend to the starry firmament. Such pursuits, while they ennoble the mind, at the same time inculcate humility, by showing that there is a barrier which no energy, mental or physical, can ever enable us to pass : that, however profoundly we may penetrate the depths of space, there still remain innumerable systems, compared with which, those apparently so vast must dwindle into insignificance, or even become invisible; and that not only man, but the globe he inhabits_nay, the whole system of which it forms so small a part —might be annihilated, and its extinction be unperceived in the immensity of creation.

A complete acquaintance with physical astronomy can be attained by those only who are well versed in the higher branches of mathematical and mechanical science (N. 2), and they alone can appreciate the extreme beauty of the results, and of the means by which these results are obtained. It is nevertheless true, that a sufficient skill in analysis (N.3) to follow the general outline—to see the mutual dependence of the different parts of the system, and to comprehend by what means the most extraordinary conclusions have been arrived at,-is within the reach of many who shrink from the task, appalled by difficulties, not more formidable than those incident to the study of the elements of every branch of knowledge. There is a wide distinction between the degree of mathematical acquirement necessary for

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