Three Scientific Revolutions: How They Transformed Our Conceptions of Reality (19 page)

Despite the nearly incontrovertible evidence, the respect for Newton was so strong that the reaction in England was hostile rather than approving. However, that changed when a gifted French engineer named Augustine Jean Fresnel, having had doubts about the corpuscular theory and impressed by the results of Young's experiments, decided to test whether Newton's generally accepted explanation was true. His explanation was that the wave bands were produced by the attractive or repelling effects of the shapes and thickness of the apertures on the light corpuscles as they passed through. But when Fresnel, based on experiments that varied the shapes and thickness of the tiny openings, found they had no effect on the diffraction patterns that depended solely on the size of the aperture, even the English were converted. When he presented the results of his experiments in a “Memoir on the Diffraction of Light” to the Paris Academy in 1819, he was awarded a prize.

It was Fresnel's ability to quantify his results and predict additional testable consequences that was particularly convincing. As an example, rejecting Newton's peculiar explanation of the polarization of light rays emerging from Iceland spar by attributing it to different sides of the corpuscles constituting the light rays, he concluded that the wave theory could provide a simpler and more plausible explanation if one accepted that the light waves were transverse, produced by the perpendicular vibrations upward and downward of the undulations emitted from the apertures. Thus Fresnel's explanation proved to be a final vindication of Hooke's and Huygens's advocacy of the wave conception of light.

Then Jean Léon Foucault, in addition to demonstrating the rotation of the earth by hanging a huge pendulum from the roof of the Panthéon in Paris in 1851 and inventing the gyroscope, in what is often referred to as an
experimentum crucis
, by exacting experiments begun in 1850 and confirmed in 1862, he demonstrated that light travels more slowly in denser media, thereby disproving Newton's prediction that it would travel faster due to the greater attractive force of the more dense media on the corpuscles. This was the final blow to the corpuscular theory because nothing is more fatal to a theory than a definite disconfirmation of a crucial prediction.

Furthermore, based on Foucault's experiments, Hippolyte Louis Fizeau determined the velocity of light to be 300,000 kilometers per second, thus settling the dispute as to whether light was transmitted instantaneously, as many had believed, or with a finite velocity. So by mid-century, owing to these ingenious experiments confirming the properties of light, most scientists accepted the wave theory over Newton's corpuscular theory. One would have to await Einstein's 1905 paper explaining the photoelectric effect in terms of discrete quanta of light before the particulate properties of light would again be accepted.

There is a further aspect to the discussion, the existence of the aether. Unlike the transmission of corpuscles, waves being a configuration of a medium required the existence of a medium that later was called “aether.” Although in Newton's corpuscular theory light did not require a medium for its transmission, in the long quote in the previous chapter on Newton he did predict that in the future a unified theory would be developed to explain all the various astronomical, physical, chemical, optical, and even neurological phenomena in one integrated theoretical framework.

Yet nothing illustrates more clearly the difficulty that such transitions present than the fact that even someone of Newton's genius could not make a complete break with the older tradition. He continued to describe the underlying unifying force as due to the “vibrations” of an “a certain most subtle spirit”
⁶⁰
that conflicted with his criticism of “feigned hypotheses” and astute definition of the correct scientific method. Nevertheless, the concept of an electric spirit required for the transmission of electricity and possessing the vibratory elasticity needed for the transmission of light waves would soon be replaced by an all pervasive subtle medium called the “aether,” that in turn would be replaced later by Einstein's concept of a space-time field. Such are the contingent fortunes of scientific theories owing to the continuous experimental testing of past theories. But despite the almost universal acceptance of the aether theory, the discovery of electromagnetism, radiation, and the invariant velocity of light, the explanatory value of the aether became nil and was discarded after the Michelson-Morely experiments and Einstein's Special Theory of Relativity proved the invariant velocity of light.

Turning now to another scientific revolution that would contest Newton's mechanistic worldview, though it had been previously suspected that electricity and magnetism were not independent, it was Hans Christian Oersted in 1807 who demonstrated their interconnectedness. Investigating the effects of an electric current on the deflection of a magnetic needle, he discovered that
a changing current
induced a magnetic field and announced his discovery in an article titled
Experimenta circa effectum conflictus electrici in acum maneticam
in 1820.

Describing it as “the
conflict of electricity
,” he wrote that the magnetic field produced by the electric wire occupied a curved space surrounding the magnet, whose direction was dependent upon whether the wire was above or below the needle along with the direction of the current. The French academician François Arago, upon learning of Oersted's experiments, devised his own experiment in 1820 showing that when a current is passed though a circular copper wire it attracts unmagnetized iron filings that remain attracted to the wire as long as it is electrified, but immediately fall off when the current ceases. Then in 1824 he reported that a rotated copper disk produced a similar rotation of a magnetic needle supported above it.

Another major contributor, Andre Marie Ampère, shortly after Oersted's publications, proposed the laws governing the electric current's deflection of the magnetic needle, along with the reciprocal attractions and repulsions of electric currents. His outstanding achievements are memorialized in the “well-known ‘Ampère's Rule', formulated by him for determining the deflection of a magnet by an electric current, and in the
ampere
, the practical unit of electric current, which is named after him.”
⁶¹

Next in the succession of contributors is Michael Faraday, referred to by British historian of science Charles A. Singer as “one of the greatest of scientific geniuses,” introduced the concept of a “field of force” to describe the magnetic aura created by a current from an electrified wire. Just as Ampère had demonstrated that a spherical coil of wire produces a magnetic attraction when a current is passed through it, Faraday in a series of experiments demonstrated the converse—that moving magnets could “induce” an electric current. Realizing that “the essential factor in the production of the magneto-electric effects was change, movement of the magnet or of the coil, or making and breaking of the current or the contact,” he concluded that they are what produce the “fields of force” (p. 363). This discovery of electro-magnetic induction resulted in the invention of the dynamo and the production of electricity on such a large scale that it transformed civilization. We have become so dependent upon readily available electricity that whenever there is a loss of electricity in the Western world due to some natural disaster or snow storm life becomes chaotic.

While Faraday's great contribution was the experimental discovery of what generated the magneto-electric currents, it was James Clerk Maxwell who, by his equations describing the structure and changes of the “electromagnetic field,” fully developed the theory of electromagnetism that had been confirmed by Heinrich Hertz at the end of the nineteenth century. In his work
On a Dynamical Theory of the Electro-magnetic Field
, published in 1864, Maxwell declared that since the electromagnetic waves were transverse analogous to light and had the same velocity as light, the latter must also be a form of electromagnetism. It was this that led Einstein and Infeld to declare that the “theoretical discovery of an electromagnetic wave spreading with the speed of light is one of the greatest achievements in the history of science.”

The next advance was the experimental attempt to discover the interior structure of the atom. In our previous discussion of atomism it was pointed out how the recognition of oxygen's role in combustion by Lavoisier led to the development of chemistry and the identification of additional elements such as hydrogen and nitrogen, followed by Dalton's and Berzelius's determination, based on their atomic weights, of the ratios of the elements constituting the molecular structure of substances such as air and water. This culminated in Meyer's and Mendeleev's organization of the elements into the Periodic Table based on the periodicity of their properties according to their atomic weights. At the time, the assumption was that the monatomic elements were internally compact and therefore indivisible as was believed by Leucippus and Democritus, the originators of atomism. Their observable properties were explained by their sizes, shapes, mass, weight, and motion.

There had been some indications, however, that that this was not true. Even as early as the fourth century BCE, Epicurus had conjectured that the various sizes and shapes of atoms might be due to internal “minima,” which, like present-day quarks, could not exist separately. And even Newton in Query 8 of the
Opticks
, had asked: “Do not all fix's Bodies, when heated beyond a certain degree, emit Light and shine; and is not this Emission perform'd by the vibrating motion of its parts?” Newton also deduced that the produced light consisted of identifying emissions, a process now called spectral analysis or spectroscopy, that provides a more extensive and accurate identification of their unique chemical properties. Even though his mechanistic explanation—that it was the vibratory or oscillatory frequencies of the atoms or molecules caused by the heat that produced the emissions—was mistaken, his suggestion that heated objects or other substances produce identifying spectra introduced a new method for analyzing the properties of phenomena and opened up a whole new area of scientific enquiry.

One of the first to pursue the inquiry was Thomas Melville who discovered the spectrum of salt, while William Wollaston and Joseph von Fraunhofer initiated the science of astrophysics when, in 1802, Wollaston started examining the solar spectrum and Fraunhofer invented the spectroscope in 1814 for mapping the latter. Discovering that basic gases can also be identified by their signature spectrum, Anders Jöns Ångström observed the spectrum of hydrogen and, with Julius Plücker, computed the wavelengths of the four spectral emissions of hydrogen.

But it was Gustav Robert Kirchhoff and Robert Bunsen—the latter having invented the burners needed to produce a pure flame required for the spectral analysis, which is still used in chemistry laboratories today—who largely created the science of spectroscopy by definitely establishing in 1859 that each chemical substance emits its own signature spectrum. Even though the evidence was more complex than they originally believed, since at higher temperatures substances produce different line spectra, they realized that the method could be used to discover new elements to fill the gaps in the Periodic Table.

In a joint statement they described the purpose and nature of their “spectrum-analytic method.”

In spectrum analysis . . . the colored lines appear unaffected by . . . external influences and unchanged by the intervention of other materials. The positions occupied [by the lines] in the spectrum determine a chemical property of a similar unchangeable and fundamental nature as the atomic weight . . . with an almost astronomical accuracy. What gives the spectrum-analytic method a quite special significance is . . . that it extends in an almost unlimited way the limits imposed up till now on the chemical characterization of matter.
⁶²

Although spectral analysis would prove limited in physics and chemistry with the discovery of the inner structure of the atom, solar and stellar spectral analysis has provided our main information about the composition of the planets, comets, and other astronomical phenomena.

But along with spectral analysis, electrical developments before the discovery of subatomic particles provided additional understanding of electrical conduction and radiation and facilitated the discovery of the charged subatomic particles. For example, Michel Faraday constructed the cathode ray tube for investigating electrical discharges in gases. In vacuum tube experiments conducted between 1833 and 1838, he passed a current from a negative electrode or cathode to a positive electrode or anode through which rarified gases passed. This induced a glow on the inner surface of the opposite end of the tube.

The glow resembling that of phosphorescence, scientists were perplexed by what caused the luminosity. Because the effectiveness of the experiments depended upon the extent of the vacuum and the strength of the current, Johann Hittorf , Philipp Lenard, and Sir William Crookes performed numerous experiments to improve its effectiveness. Then Heinrich Rühmkorff introduced a better induction coil to generate higher voltage that produced stronger currents in the vacuum tube.

The reason for describing these experiments is their influence on later emission research. For example, intrigued by the previous experiments on cathode ray tubes, Wilhelm Röntgen, in repeating those experiments, discovered a ray with an amazing penetrating power. Experimenting in a dark room on November 8, 1895, having completely covered a Hittorf cathode tube with a black cardboard to block any rays, he suddenly noticed that a sheet of paper coated with barium platinum-cyanide, located a short distance from the cathode tube, fluoresced indicating that some rays must have penetrated the cardboard and activated the coating thereby producing the glow. He was especially astonished when he held his hand between the tube and the coated paper and saw that the rays penetrated his hand except where obstructed by the bones and a ring on his finger. He later produced a dramatic photograph of his skeletal hand during the announcement of his discovery of what he called X-rays, because of their mysterious penetrating power. For this work he was awarded the first Nobel Prize in physics in 1901.