What Romantics, or nature philosophers, as they called themselves, could see that was hidden from their Newtonian colleagues was demonstrated by Hans Christian Ørsted. He found it impossible to believe that there was no connection between the forces of nature. Chemical affinity, electricity, heat, magnetism, and light must, he argued, simply be different manifestations of the basic forces of attraction and repulsion. In 1820 he showed that electricity and magnetism were related, for the passage of an electrical current through a wire affected a nearby magnetic needle. This fundamental discovery was explored and exploited by Michael Faraday, who spent his whole scientific life converting one force into another. By concentrating on the patterns of forces produced by electric currents and magnets, Faraday laid the foundations for field theory, in which the energy of a system was held to be spread throughout the system and not localized in real or hypothetical particles.
The transformations of force necessarily raised the question of the conservation of force. Is anything lost when electrical energy is turned into magnetic energy, or into heat or light or chemical affinity or mechanical power? Faraday, again, provided one of the early answers in his two laws of electrolysis, based on experimental observations that quite specific amounts of electrical “force” decomposed quite specific amounts of chemical substances. This work was followed by that of James Prescott Joule, Robert Mayer, and Hermann von Helmholtz, each of whom arrived at a generalization of basic importance to all science, the principle of the conservation of energy.
The nature philosophers were primarily experimentalists who produced their transformations of forces by clever experimental manipulation. The exploration of the nature of elemental forces benefitted as well from the rapid development of mathematics. In the 19th century the study of heat was transformed into the science of thermodynamics, based firmly on mathematical analysis; the Newtonian corpuscular theory of light was replaced by Augustin-Jean Fresnel’s mathematically sophisticated undulatory theory; and the phenomena of electricity and magnetism were distilled into succinct mathematical form by William Thomson (Lord Kelvin) and James Clerk Maxwell. By the end of the century, thanks to the principle of the conservation of energy and the second law of thermodynamics, the physical world appeared to be completely comprehensible in terms of complex but precise mathematical forms describing various mechanical transformations in some underlying ether.
The submicroscopic world of material atoms became similarly comprehensible in the 19th century. Beginning with John Dalton’s fundamental assumption that atomic species differ from one another solely in their weights, chemists were able to identify an increasing number of elements and to establish the laws describing their interactions. Order was established by arranging elements according to their atomic weights and their reactions. The result was the periodic table, devised by Dmitry Mendeleyev, which implied that some kind of subatomic structure underlay elemental qualities. That structure could give rise to qualities, thus fulfilling the prophecy of the 17th-century mechanical philosophers, was shown in the 1870s by Joseph-Achille Le Bel and Jacobus van ’t Hoff, whose studies of organic chemicals showed the correlation between the arrangement of atoms or groups of atoms in space and specific chemical and physical properties. The founding of modern biology
The study of living matter lagged far behind physics and chemistry, largely because organisms are so much more complex than inanimate bodies or forces. Harvey had shown that living matter could be studied experimentally, but his achievement stood alone for two centuries. For the time being, most students of living nature had to be content to classify living forms as best they could and to attempt to isolate and study aspects of living systems.
As has been seen, an avalanche of new specimens in both botany and zoology put severe pressure on taxonomy. A giant step forward was taken in the 18th century by the Swedish naturalist Carl von Linné—known by his Latinized name, Linnaeus—who introduced a rational, if somewhat artificial, system of binomial nomenclature. The very artificiality of Linnaeus’s system, focusing as it did on only a few key structures, encouraged criticism and attempts at more natural systems. The attention thus called to the organism as a whole reinforced a growing intuition that species are linked in some kind of genetic relationship, an idea first made scientifically explicit by Jean-Baptiste, chevalier de Lamarck.
Problems encountered in cataloging the vast collection of invertebrates at the Museum of Natural History in Paris led Lamarck to suggest that species change through time. This idea was not so revolutionary as it is usually painted, for, although it did upset some Christians who read the book of Genesis literally, naturalists who noted the shading of natural forms one into another had been toying with the notion for some time. Lamarck’s system failed to gain general assent largely because it relied upon an antiquated chemistry for its causal agents and appeared to imply a conscious drive to perfection on the part of organisms. It was also opposed by one of the most powerful paleontologists and comparative anatomists of the day, Georges Cuvier, who happened to take Genesis quite literally. In spite of Cuvier’s opposition, however, the idea remained alive and was finally elevated to scientific status by the labours of Charles Darwin. Darwin not only amassed a wealth of data supporting the notion of transformation of species, but he also was able to suggest a mechanism by which such evolution could occur without recourse to other than purely natural causes. The mechanism was natural selection, according to which minute variations in offspring were either favoured or eliminated in the competition for survival, and it permitted the idea of evolution to be perceived with great clarity. Nature shuffled and sorted its own productions, through processes governed purely by chance, so that those organisms that survived were better adapted to a constantly changing environment.
Darwin’s On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, published in 1859, brought order to the world of organisms. A similar unification at the microscopic level had been brought about by the cell theory announced by Theodor Schwann and Matthias Schleiden in 1838, whereby cells were held to be the basic units of all living tissues. Improvements in the microscope during the 19th century made it possible gradually to lay bare the basic structures of cells, and rapid progress in biochemistry permitted the intimate probing of cellular physiology. By the end of the century the general feeling was that physics and chemistry sufficed to describe all vital functions and that living matter, subject to the same laws as inanimate matter, would soon yield up its secrets. This reductionist view was triumphantly illustrated in the work of Jacques Loeb, who showed that so-called instincts in lower animals are nothing more than physicochemical reactions, which he labelled tropisms.
The most dramatic revolution in 19th-century biology was the one created by the germ theory of disease, championed by Louis Pasteur in France and Robert Koch in Germany. Through their investigations, bacteria were shown to be the specific causes of many diseases. By means of immunological methods first devised by Pasteur, some of humankind’s chief maladies were brought under control. The 20th-century revolution
By the end of the 19th century, the dream of the mastery of nature for the benefit of humankind, first expressed in all its richness by Sir Francis Bacon, seemed on the verge of realization. Science was moving ahead on all fronts, reducing ignorance and producing new tools for the amelioration of the human condition. A comprehensible, rational view of the world was gradually emerging from laboratories and universities. One savant went so far as to express pity for those who would follow him and his colleagues, for they, he thought, would have nothing more to do than to measure things to the next decimal place.