REFERENCES FOR READING

CLERKE. History of Astronomy during the Nineteenth Century.

CLERKE.

HALE.

The Herschels and Modern Astronomy.

Stellar Evolution.

LODGE. Pioneers of Science.

MACH. Science of Mechanics.

MERZ. History of European Thought in the Nineteenth Century, Chapters

IV, V.

WHITEHEAD. Introduction to Mathematics.

POINCARE. Science and Hypothesis.

CHAPTER XVI

SOME ADVANCES IN PHYSICAL SCIENCE IN THE NINETEENTH CENTURY. ENERGY AND

THE CONSERVATION OF ENERGY

About a century after the publication of the Principia, which, by propounding the gravitation formula, raised the ancient and indefinite notion of Attraction to the rank of a useful and rigorously defined expression, another favorite theory [Atomism] of the ancient philosophers was similarly elevated to the rank of a leading and useful scientific idea.

The law of gravitation embraced cosmical and some molar phenomena, but led to vagueness when applied to molecular actions. The atomic theory led to a complete systematization of chemical compounds, but afforded no clue to the mysteries of chemical affinity. And the kinetic or mechanical theories of light, of electricity and magnetism, led rather to a new dualism, the division of science into sciences of matter and of the ether. . . . A more general term had to be found under which the different terms could be comprised, which would give a still higher generalization, a more complete unification of knowledge. One of the principal performances of the second half of the nineteenth century has been to find this more general term, and to trace its all-pervading existence on a cosmical, a molar, and a molecular scale... this greatest of all exact generalizations — the conception of energy.

Electrified and magnetised bodies attract or repel each other according to laws discovered by men who never doubted that the action took place at a distance, without the intervention of any medium, and who would have regarded the discovery of such a medium as complicating rather than as explaining the undoubted phenomena of attraction. Merz.

Through metaphysics first; then through alchemy and chemistry, through physical and astronomical spectroscopy, lastly through radio-activity, science has slowly groped its way to the atom. Soddy.

There is in nature a certain magnitude of unsubstantial quality, which keeps its value under all alterations of the objects observed, while its manner of appearance changes most variously. — Mayer.

I shall lose no time in repeating and extending these experiments, being satisfied that the grand agents of nature are, by the Creator's fiat, indestructible; and that whatever mechanical force is expended, an exact equivalent of heat is always obtained. -Joule.

Heat and work are equivalent. The entropy of the universe tends to a maximum. - Clausius.

The later eighteenth and the whole of the nineteenth centuries are characterized by increasingly rapid development of the physical sciences, which become more and more completely differentiated, and more and more important in their influence upon industry and civilization. While it is evidently impossible within our available space to describe all phases of this varied development, we shall attempt to enumerate some of those which are most general in their character and most far-reaching in their consequences. A relatively complete and highly instructive review of the whole subject may be found in Merz's History of European Thought in the Nineteenth Century.

At the beginning of this century mathematics was in a stage of triumphant expansion, in which the related sciences of astronomy and mechanics participated. General physics and chemistry were still in the preliminary stage of collecting and coördinating data, with attempts at quantitative interpretation, while in their train the natural sciences were following somewhat haltingly.

The most notable advance in physical science during the century is the gradual working out of the great fundamental principle of the conservation of energy, affecting profoundly the whole range of phenomena. Of equal or even greater-importance is the gradual realization of progressive development — evolution not only in plant and animal life but even in the inorganic world. Physics is gradually enriched by experimental researches and by the working out of mathematical theories of heat, light, magnetism and electricity. Chemistry, largely hitherto a collection of unrelated facts, becomes more and more coördinated with

physics and mathematics by means of the spectroscope, the principle of the conservation of energy, the atomic theory, the kinetic theory of gases, and the study of molecular structure. On the other hand, its relations with the organic world are made more clear through the investigation of the compounds of carbon.

All other sciences, pure and applied, as well as the industries, profit unexpectedly and almost inconceivably by these nineteenth century advances in physics and chemistry. The older observational and mathematical astronomy achieves a marvellous triumph in the discovery of a new planet Neptune, as related in Chapter XV, and even this is soon rivalled by the startling achievements of the new physical and chemical astronomy.

Reserving for the following chapter a sketch of the development of the natural sciences under the ultimately dominant influence of the theory of evolution, we proceed to outline briefly some of the more notable advances in the physical sciences.

MODERN PHYSICS. Some of the main features in the development of physics in the nineteenth century have been :-the working out of consistent theories of light and radiant heat as wave phenomena of a peculiar hypothetical medium called the "ether"; the extensive investigation of electrical and magnetic phenomena and the development of an electromagnetic theory even so far as to include optics; the working out of a kinetic theory of gases with important relations to chemical as well as physical theory; the elaboration of general theories of matter, force, and energy, all culminating in the crowning discovery of the great unifying principle of the Conservation of Energy.

HEAT, THERMOMETRY: CARNOT, RUMFORD. - The invention of the thermometer has been traced in Chapter XII. To the nineteenth century belongs the determination of an absolute scale 1as distinguished from the arbitrary one previously employed. The idea that heat is not a substance but a mode of molecular motion arose in the seventeenth and eighteenth centuries, but was

1

1 The absolute scale is based on the indirect determination of a temperature (-273° Centigrade =-459° Fahrenheit) at which the internal activity which constitutes heat is supposed to cease.

first given a substantial experimental basis by the researches of Benjamin Thompson, Count Rumford (1753–1814), who showed that by friction of two bodies an unlimited amount of heat could be generated. His results were reported to the Royal Society in 1798.

Rumford made a cylinder of gun-metal rotate in a box containing water, and by the friction of a revolving borer driven by horsepower the water was heated to boiling in two and a half hours. Deeply impressed he exclaims:

What is heat? Is there any such thing as an igneous fluid? ... Anything which any insulated body, or system of bodies, can continue to furnish without limitation, cannot possibly be a material substance; and it appears to me to be extremely difficult, if not quite impossible, to form any distinct idea of anything, capable of being excited, and communicated, in the manner the heat was excited and communicated in these experiments, except it be MOTION.

The "mechanical equivalent of heat"-i.e. the work required to heat one pound of water one degree-was roughly calculated. Epoch-making in the theory of heat were the researches of Sadi Carnot (1796-1832), whose words follow:

Wherever there is a difference of temperature followed by return to equilibrium the generation of power may take place. Water vapor is one means, but not the only one. A solid body, for example a metal bar, gains and loses in length when it is alternately heated and cooled, and thus is able to move bodies fastened to its ends. . . .

The whole process he pictures as a cycle in which a certain portion of the heat applied is converted into work, a certain other portion being lost. Thus the new science of thermodynamics was born. The thorough and complete investigation of the "mechanical equivalent of heat" belongs to J. P. Joule (1818-1889) of Manchester, England, a pupil of Dalton the chemist.

LIGHT; WAVE THEORY, VELOCITY: YOUNG, FRESNEL.- As stated in Chapter XIV Huygens had supported a wave theory of light, while Newton accepted an emission theory. That sound was propagated by atmospheric waves was well known. There was a troublesome contrast however in the phenomenon of shadows.