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The 17th century was a time of intense religious feeling, and nowhere was that feeling more intense than in Great Britain. There a devout young man, Isaac Newton, was finally to discover the way to a new synthesis in which truth was revealed and God was preserved.
Newton was both an experimental and a mathematical genius, a combination that enabled him to establish both the Copernican system and a new mechanics. His method was simplicity itself: “from the phenomena of motions to investigate the forces of nature, and then from these forces to demonstrate the other phenomena.” Newton’s genius guided him in the selection of phenomena to be investigated, and his creation of a fundamental mathematical tool—the calculus (simultaneously invented by Gottfried Leibniz)—permitted him to submit the forces he inferred to calculation. The result was Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy, usually called simply the Principia), which appeared in 1687. Here was a new physics that applied equally well to terrestrial and celestial bodies. Copernicus, Kepler, and Galileo were all justified by Newton’s analysis of forces. Descartes was utterly routed.
Newton’s three laws of motion and his principle of universal gravitation sufficed to regulate the new cosmos, but only, Newton believed, with the help of God. Gravity, he more than once hinted, was direct divine action, as were all forces for order and vitality. Absolute space, for Newton, was essential, because space was the “sensorium of God,” and the divine abode must necessarily be the ultimate coordinate system. Finally, Newton’s analysis of the mutual perturbations of the planets caused by their individual gravitational fields predicted the natural collapse of the solar system unless God acted to set things right again.
The diffusion of scientific method
The publication of the Principia marks the culmination of the movement begun by Copernicus and, as such, has always stood as the symbol of the scientific revolution. There were, however, similar attempts to criticize, systematize, and organize natural knowledge that did not lead to such dramatic results. In the same year as Copernicus’s great volume, there appeared an equally important book on anatomy: Andreas Vesalius’s De humani corporis fabrica (“On the Fabric of the Human Body,” called the De fabrica), a critical examination of Galen’s anatomy in which Vesalius drew on his own studies to correct many of Galen’s errors. Vesalius, like Newton a century later, emphasized the phenomena—i.e., the accurate description of natural facts. Vesalius’s work touched off a flurry of anatomical work in Italy and elsewhere that culminated in the discovery of the circulation of the blood by William Harvey, whose Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (An Anatomical Exercise Concerning the Motion of the Heart and Blood in Animals) was published in 1628. This was the Principia of physiology that established anatomy and physiology as sciences in their own right. Harvey showed that organic phenomena could be studied experimentally and that some organic processes could be reduced to mechanical systems. The heart and the vascular system could be considered as a pump and a system of pipes and could be understood without recourse to spirits or other forces immune to analysis.
In other sciences the attempt to systematize and criticize was not so successful. In chemistry, for example, the work of the medieval and early modern alchemists had yielded important new substances and processes, such as the mineral acids and distillation, but had obscured theory in almost impenetrable mystical argot. Robert Boyle in England tried to clear away some of the intellectual underbrush by insisting upon clear descriptions, reproducibility of experiments, and mechanical conceptions of chemical processes. Chemistry, however, was not yet ripe for revolution.
In many areas there was little hope of reducing phenomena to comprehensibility, simply because of the sheer number of facts to be accounted for. New instruments like the microscope and the telescope vastly multiplied the worlds with which humans had to reckon. The voyages of discovery brought back a flood of new botanical and zoological specimens that overwhelmed ancient classificatory schemes. The best that could be done was to describe new things accurately and hope that someday they could all be fitted together in a coherent way.
The growing flood of information put heavy strains upon old institutions and practices. It was no longer sufficient to publish scientific results in an expensive book that few could buy; information had to be spread widely and rapidly. Nor could the isolated genius, like Newton, comprehend a world in which new information was being produced faster than any single person could assimilate it. Natural philosophers had to be sure of their data, and to that end they required independent and critical confirmation of their discoveries. New means were created to accomplish these ends. Scientific societies sprang up, beginning in Italy in the early years of the 17th century and culminating in the two great national scientific societies that mark the zenith of the scientific revolution: the Royal Society of London for the Promotion of Natural Knowledge, created by royal charter in 1662, and the Académie des Sciences of Paris, formed in 1666. In these societies and others like them all over the world, natural philosophers could gather to examine, discuss, and criticize new discoveries and old theories. To provide a firm basis for these discussions, societies began to publish scientific papers. The Royal Society’s Philosophical Transactions, which began as a private venture of its secretary, was the first such professional scientific journal. It was soon copied by the French academy’s Mémoires, which won equal importance and prestige. The old practice of hiding new discoveries in private jargon, obscure language, or even anagrams gradually gave way to the ideal of universal comprehensibility. New canons of reporting were devised so that experiments and discoveries could be reproduced by others. This required new precision in language and a willingness to share experimental or observational methods. The failure of others to reproduce results cast serious doubts upon the original reports. Thus were created the tools for a massive assault on nature’s secrets.
Even with the scientific revolution accomplished, much remained to be done. Again, it was Newton who showed the way. For the macroscopic world, the Principia sufficed. Newton’s three laws of motion and the principle of universal gravitation were all that was necessary to analyze the mechanical relations of ordinary bodies, and the calculus provided the essential mathematical tools. For the microscopic world, Newton provided two methods. Where simple laws of action had already been determined from observation, as the relation of volume and pressure of a gas (Boyle’s law, pv = k), Newton assumed forces between particles that permitted him to derive the law. He then used these forces to predict other phenomena, in this case the speed of sound in air, that could be measured against the prediction. Conformity of observation to prediction was taken as evidence for the essential truth of the theory. Second, Newton’s method made possible the discovery of laws of macroscopic action that could be accounted for by microscopic forces. Here the seminal work was not the Principia but Newton’s masterpiece of experimental physics, the Opticks, published in 1704, in which he showed how to examine a subject experimentally and discover the laws concealed therein. Newton showed how judicious use of hypotheses could open the way to further experimental investigation until a coherent theory was achieved. The Opticks was to serve as the model in the 18th and early 19th centuries for the investigation of heat, light, electricity, magnetism, and chemical atoms.
The classic age of science
Mechanics
Just as the Principia preceded the Opticks, so too did mechanics maintain its priority among the sciences in the 18th century, in the process becoming transformed from a branch of physics into a branch of mathematics. Many physical problems were reduced to mathematical ones that proved amenable to solution by increasingly sophisticated analytical methods. The Swiss Leonhard Euler was one of the most fertile and prolific workers in mathematics and mathematical physics. His development of the calculus of variations provided a powerful tool for dealing with highly complex problems. In France, Jean Le Rond d’Alembert and Joseph-Louis Lagrange succeeded in completely mathematizing mechanics, reducing it to an axiomatic system requiring only mathematical manipulation.
The test of Newtonian mechanics was its congruence with physical reality. At the beginning of the 18th century it was put to a rigorous test. Cartesians insisted that the Earth, because it was squeezed at the Equator by the etherial vortex causing gravity, should be somewhat pointed at the poles, a shape rather like that of an American football. Newtonians, arguing that centrifugal force was greatest at the Equator, calculated an oblate sphere that was flattened at the poles and bulged at the Equator. The Newtonians were proved correct after careful measurements of a degree of the meridian were made on expeditions to Lapland and to Peru. The final touch to the Newtonian edifice was provided by Pierre-Simon, marquis de Laplace, whose masterly Traité de mécanique céleste (1798–1827; Celestial Mechanics) systematized everything that had been done in celestial mechanics under Newton’s inspiration. Laplace went beyond Newton by showing that the perturbations of the planetary orbits caused by the interactions of planetary gravitation are in fact periodic and that the solar system is, therefore, stable, requiring no divine intervention.
Chemistry
Although Newton was unable to bring to chemistry the kind of clarification he brought to physics, the Opticks did provide a method for the study of chemical phenomena. One of the major advances in chemistry in the 18th century was the discovery of the role of air, and of gases generally, in chemical reactions. This role had been dimly glimpsed in the 17th century, but it was not fully seen until the classic experiments of Joseph Black on magnesia alba (basic magnesium carbonate) in the 1750s. By extensive and careful use of the chemical balance, Black showed that an air with specific properties could combine with solid substances like quicklime and could be recovered from them. This discovery served to focus attention on the properties of “air,” which was soon found to be a generic, not a specific, name. Chemists discovered a host of specific gases and investigated their various properties: some were flammable, others put out flames; some killed animals, others made them lively. Clearly, gases had a great deal to do with chemistry.
The Newton of chemistry was Antoine-Laurent Lavoisier. In a series of careful balance experiments Lavoisier untangled combustion reactions to show that, in contradiction to established theory, which held that a body gave off the principle of inflammation (called phlogiston) when it burned, combustion actually involves the combination of bodies with a gas that Lavoisier named oxygen. The chemical revolution was as much a revolution in method as in conception. Gravimetric methods made possible precise analysis, and this, Lavoisier insisted, was the central concern of the new chemistry. Only when bodies were analyzed as to their constituent substances was it possible to classify them and their attributes logically and consistently.
The imponderable fluids
The Newtonian method of inferring laws from close observation of phenomena and then deducing forces from these laws was applied with great success to phenomena in which no ponderable matter figured. Light, heat, electricity, and magnetism were all entities that were not capable of being weighed—i.e., imponderable. In the Opticks, Newton had assumed that particles of different sizes could account for the different refrangibility of the various colours of light. Clearly, forces of some sort must be associated with these particles if such phenomena as diffraction and refraction are to be accounted for. During the 18th century, heat, electricity, and magnetism were similarly conceived as consisting of particles with which were associated forces of attraction or repulsion. In the 1780s, Charles-Augustin de Coulomb was able to measure electrical and magnetic forces, using a delicate torsion balance of his own invention, and to show that these forces follow the general form of Newtonian universal attraction. Only light and heat failed to disclose such general force laws, thereby resisting reduction to Newtonian mechanics.
Science and the Industrial Revolution
It has long been a commonsensical notion that the rise of modern science and the Industrial Revolution were closely connected. It is difficult to show any direct effect of scientific discoveries upon the rise of the textile or even the metallurgical industry in Great Britain, the home of the Industrial Revolution, but there certainly was a similarity in attitude to be found in science and nascent industry. Close observation and careful generalization leading to practical utilization were characteristic of both industrialists and experimentalists alike in the 18th century. One point of direct contact is known: namely, James Watt’s interest in the efficiency of the Newcomen steam engine, an interest that grew from his work as a scientific-instrument maker and that led to his development of the separate condenser that made the steam engine an effective industrial power source. But, in general, the Industrial Revolution proceeded without much direct scientific help. Yet the potential influence of science was to prove of fundamental importance.
What science offered in the 18th century was the hope that careful observation and experimentation might improve industrial production significantly. In some areas, it did. The potter Josiah Wedgwood built his successful business on the basis of careful study of clays and glazes and by the invention of instruments like the pyrometer with which to gauge and control the processes he employed. It was not, however, until the second half of the 19th century that science was able to provide truly significant help to industry. It was then that the science of metallurgy permitted the tailoring of alloy steels to industrial specifications, that the science of chemistry permitted the creation of new substances, like the aniline dyes, of fundamental industrial importance, and that electricity and magnetism were harnessed in the electric dynamo and motor. Until that period science probably profited more from industry than the other way around. It was the steam engine that posed the problems that led, by way of a search for a theory of steam power, to the creation of thermodynamics. Most importantly, as industry required ever more complicated and intricate machinery, the machine tool industry developed to provide it and, in the process, made possible the construction of ever more delicate and refined instruments for science. As science turned from the everyday world to the worlds of atoms and molecules, electric currents and magnetic fields, microbes and viruses, and nebulae and galaxies, instruments increasingly provided the sole contact with phenomena. A large refracting telescope driven by intricate clockwork to observe nebulae was as much a product of 19th-century heavy industry as were the steam locomotive and the steamship.
The Industrial Revolution had one further important effect on the development of modern science. The prospect of applying science to the problems of industry served to stimulate public support for science. The first great scientific school of the modern world, the École Polytechnique in Paris, was founded in 1794 to put the results of science in the service of France. The founding of scores more technical schools in the 19th and 20th centuries encouraged the widespread diffusion of scientific knowledge and provided further opportunity for scientific advance. Governments, in varying degrees and at different rates, began supporting science even more directly, by making financial grants to scientists, by founding research institutes, and by bestowing honours and official posts on great scientists. By the end of the 19th century the natural philosopher following his private interests had given way to the professional scientist with a public role.
The Romantic revolt
Perhaps inevitably, the triumph of Newtonian mechanics elicited a reaction, one that had important implications for the further development of science. Its origins are many and complex, and it is possible here to focus on only one, that associated with the German philosopher Immanuel Kant. Kant challenged the Newtonian confidence that the scientist can deal directly with subsensible entities such as atoms, the corpuscles of light, or electricity. Instead, Kant insisted, all that the human mind can know is forces. This epistemological axiom freed Kantians from having to conceive of forces as embodied in specific and immutable particles. It also placed new emphasis on the space between particles; indeed, if one eliminated the particles entirely, there remained only space containing forces. From these two considerations were to come powerful arguments, first, for the transformations and conservation of forces and, second, for field theory as a representation of reality. What makes this point of view Romantic is that the idea of a network of forces in space tied the cosmos into a unity in which all forces were related to all others, so that the universe took on the aspect of a cosmic organism. The whole was greater than the sum of all its parts, and the way to truth was contemplation of the whole, not analysis.
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.
