The Age of Voltaire

by Will Durant

  In 1766 Cavendish reported to the Royal Society his experiments on “factitious air”—i.e., gas derived from solids. By dissolving zinc or tin in acids he produced what he called “inflammable air”; he identified this with phlogiston; we now call it hydrogen; Cavendish was the first to recognize this as a distinct element, and to determine its specific gravity. In 1783, following up an experiment by Priestley, he found that when an electric spark was passed through a mixture of common air and “inflammable air,” part of the mixture was condensed into dew; he concluded from this electrolysis that water is composed of 2.014 volumes of “inflammable air” to one volume of Priestley’s “dephlogisticated air”—or, as we now say, H20; this was the first definite proof that water is a compound, not an element. (James Watt independently suggested the same composition of water in that same year 1783.) Again applying an electric spark to a mixture of hydrogen with common air, Cavendish obtained nitric acid, and concluded that pure air is composed of oxygen and nitrogen. (Daniel Rutherford of Edinburgh had discovered nitrogen as a distinct element in 1772.) Cavendish admitted a small residue which he could not explain, but which he calculated to be 0.83 per cent of the original amount. This remained a mystery till 1894, when Rayleigh and Ramsay isolated this part, now called argon, as a separate element, and found it to be by weight 0.94 per cent common air. Cavendish’s scales were justified.

  3. Lavoisier

  Meanwhile, across the Channel, a group of enthusiastic researchers gave France the lead in the new science, and gave chemistry essentially the form that it has today. At their source stood Guillaume Rouelle, distinguished for his work on the chemistry of salts, but best known for the lecture courses in which he taught chemistry to rich and poor, to Diderot and Rousseau, and to the greatest chemist of them all.

  Antoine Lavoisier had the advantage or handicap of being born to wealth (1743). His father, an advocate in the Paris Parlement, gave the boy all the education then available, and bequeathed to him, then twenty-three years old, 300,000 livres. Such a fortune could have aborted a literary career, but it was a help in a science that demanded expensive apparatus and long years of preparation. Sent to a law school, Antoine escaped from it into mathematics and astronomy, and attended Rouelle’s lectures in the auditorium of the Jardin du Roi. Nevertheless he completed his law studies, and then accompanied Jean Guettard in making mineralogical tours and maps of France. In 1768 he was elected to the Académie des Sciences, which at that time included Buffon, Quesnay, Turgot, and Condorcet. A year later he joined the farmers general in their unpopular business of collecting excise taxes to reimburse themselves for their advances to the government. He paid 520,000 livres for a third interest in one of the sixty shares of the ferme générale; in 1770 he raised this to a full share. In 1771 he married Marie Paulze, daughter of a rich farmer general. He spent part of his time now in traveling through the provinces, collecting revenue, tax data, and geological specimens. His wealth financed a great laboratory and costly experiments,III but it brought him to the guillotine.

  He took an active part in public affairs. Appointed (1775) régisseur des poudres, commissioner of gunpowder, he increased the production and improved the quality of that explosive, making possible its large-scale export to the American colonies and the victories of the French Revolutionary armies. “French gunpowder,” said Lavoisier in 1789, “has become the best in Europe.… One can say with truth that to it North America owes its liberty.”43 He served on a variety of official boards, national or municipal, and met with versatile intelligence diverse problems of taxation, coinage, banking, scientific agriculture, and public charity. As a member of the provincial assembly at Orléans (1787) he labored to better economic and social conditions. During the critical food shortage of 1788 he advanced his own money to several towns for the purchase of grain. He was a public-spirited man who kept on making money.

  Amid all these activities he did not cease to be a scientist. His laboratory became the most complex and extensive before the nineteenth century: 250 instruments, thirteen thousand glass containers, thousands of chemical preparations, and three precision balances that later helped to determine the gram as the unit of weight in the metric system. Weighing and measuring were half the secret of Lavoisier’s discoveries; through them he changed chemistry from a qualitative theory to a quantitative science. It was by careful weighing that he proved Stahl’s phlogiston to be an encumbering myth. That myth had assumed the existence of a mysterious substance which in combustion left the burning material and entered the air. On November 1, 1772, Lavoisier submitted to the Académie des Sciences a note that read:

  About eight days ago I discovered that sulfur in burning, far from losing weight, rather gains it; that is to say, that from a pound of sulfur may be obtained more than a pound of vitriolic acid, allowance being made for the moisture of the air. It is the same in the case of phosphorus. The gain in weight comes from the prodigious quantity of air which is fixed [i.e., absorbed by the burning matter] during the combustion, and combines with the [vitriolic] vapors. This discovery, which I have established by experiments that I consider decisive, has made me believe that what is observed in the combustion of sulfur and phosphorus may equally well take place in the case of all those bodies which gain weight on combustion or calcination.44

  Instead of the burning material giving something to the air, it took something from the air. What was this something?

  In the fall of 1774 Lavoisier published an account of further experiments. He put a weighed quantity of tin into a weighed flask large enough to contain considerable air; he sealed the flask, and heated the whole till the tin had been well oxidized. Having allowed the system to cool, he found that its weight remained unchanged. But when he broke the seal air rushed into the flask, indicating that a partial vacuum had been created in the flask. How? Lavoisier saw no other explanation except that the burning tin had absorbed into itself a part of the air. What was this something?

  In October, 1774, Lavoisier met Priestley in Paris. Priestley told him of the experiments he had made in August, which Priestley still interpreted as showing an escape of phlogiston from the burned substance into the air. On April 26, 1775, Lavoisier read to the Académie a memoir reporting the experiments that had led him to view combustion as the absorption, by a burning substance, of a mysterious element from the air, which he provisionally called air éminemment pur. Like Priestley, he had discovered oxygen; unlike Priestley, he had overthrown the phlogiston myth. Not till 1779 did he coin, for the combustible element in the air, the name oxygène, from Greek words meaning “acid-generator,” for Lavoisier mistakenly believed that oxygen was an indispensable constituent of all acids.

  Like Priestley, Lavoisier observed that the kind of air absorbed by metals in combustion is also the kind that best supports animal life. On May 3, 1777, he presented to the Académie a paper “On the Respiration of Animals.” “Five sixths of the air we breathe,” he reported, “is incapable of supporting the respiration of animals, or ignition and combustion; … one fifth only of the volume of atmospheric air is respirable.” He added that “an air which has for some time served to support this vital function has much in common with that in which metals have been calcined [oxidized]; knowledge of the one [process] may naturally be applied to the other” Lavoisier thereupon founded organic analysis by describing respiration as the combination of oxygen with organic matter. In this process he noted a liberation of heat, as in combustion; and he further confirmed the analogy of respiration and combustion by showing that carbon dioxide and water are given off (as in respiration) by the burning of such organic substances as sugar, oil, and wax. The science of physiology was now revolutionized by the spreading interpretation of organic processes in physicochemical terms.

  The multiplication of experiments, the growth of chemical knowledge, and the abandonment of the phlogiston theory required a new formulation, and a new nomenclature, for the burgeoning science. The Académie des Sciences appointed Lavoisier, Gu
yton de Morveau, Fourcroy, and Berthollet to attempt this task. In 1787 they published Méthode d’une nomenclature chimique. Old-fashioned names like powder of algaroth, butter of arsenic, and flowers of zinc were discarded; dephlogisticated air became oxygen; phlogisticated air became azote, then nitrogen; inflammable gas became hydrogen; fixed air became carbon acid gas; calcination became oxidation, compounds were named from their components. A table of “simple substances” listed thirty-two elements known to Lavoisier; chemists now list ninety-eight. Most of the terms adopted in the Méthode are standard in chemical terminology today. Lavoisier presented the new nomenclature, and summed up the new science, in his Traité élémentaire de chimie; this appeared in 1789, and marked another revolution—the end of Stahl’s phlogiston and Aristotle’s elements.

  Lavoisier himself was a victim of the French Revolution. He had shared in the efforts to avoid it, and in the evils that brought it on. In the decade that prepared it he served zealously on commissions to study and correct abuses in prisons and hospitals. To Comptroller General Laurent de Villedeuil he presented (1787) a memoir listing nine factors in the exploitation of the peasantry. His words were especially honorable coming from a millionaire owner of land:

  Let us be bold enough to say that … until the reign of Louis XVI the people counted for nothing in France; it was only the power, the authority, and the wealth of the state that were considered; the happiness of the people, the liberty and well-being of the individual, were words that never fell upon the ears of our former rulers, who were not aware that the real object of government must be to increase the sum total of enjoyment, happiness, and welfare of all its subjects.… The unfortunate farmer groans in his cottage, unrepresented and undefended, his interests cared for by none of the great departments of the national administration.45

  Lavoisier was chosen to represent the Third Estate at the provincial assembly that met at Orléans in 1787. There he offered a measure for abolishing the corvée and for maintaining the roads not by the forced labor of the peasantry but by taxes levied on all classes; the nobility and the clergy defeated this proposal. He recommended a system of social security by which all Frenchmen who so wished would contribute to support their old age; this too was defeated. In a memoir addressed to the government in 1785 he laid down the principle that the coming States-General should have full legislative power, the king to be merely its executive agent; that it should be convoked regularly; that taxation should be universal, and the press free:46 Lavoisier was unquestionably one of the most enlightened members of the French bourgeoisie, and probably his proposals expressed part of its political strategy.

  He was also one of the leading members of the ferme générale, which was the object of almost universal resentment. From 1768 to 1786 his profits as a farmer general had averaged 66,667 livres per year, an annual rate of 8.28 per cent; he may have been right in considering this a reasonable return for the labor and risks involved. It was at his suggestion that chief minister Calonne, in 1783–87, built a wall around Paris to check the smugglers who were evading tolls; the wall and the new customshouses and barriers cost thirty million livres, and evoked widespread condemnation; the Duc de Nivernois proclaimed that the originator of the scheme should be hanged.

  Lavoisier supported the Revolution in 1789, when it was still under control by the middle classes. A year later he felt that it was moving toward excess, violence, and war, and he pleaded for restraint. In November some employees of the ferme générale published a pamphlet accusing the ferme of embezzling their pension fund. “Tremble,” they wrote, “you who have sucked the blood of the unfortunate.”47 In 1791 Marat began a personal campaign against Lavoisier. The “Friend of the People” had published in 1780 Recherches physiques sur le feu, in which he claimed to have made visible the secret element in fire; Lavoisier had refused to take the claim seriously; Marat had not forgotten. In his periodical, Ami du peuple, January 27, 1791, Marat denounced the chemist-financier as a charlatan with a fat income, a man “whose only claim to public recognition is that he put Paris in prison by cutting off the fresh air with a wall that cost the poor 33 million livres.… Would to Heaven that he had been strung up to the lamppost.”48 On March 20, 1791, the Constituent Assembly abolished the ferme générale.

  Next to be attacked was the Académie des Sciences, for all institutions surviving from the Old Regime were suspected of counterrevolutionary sympathies. Lavoisier defended the Académie, and became the chief target. On August 8, 1793, the Académie was ordered to disband. At its last meeting the roster was signed by, among others, Lagrange, Lavoisier, Lalande, Lamarck, Berthollet, and Monge. Each now went his own way, hoping that the guillotine would not find him.

  In the same month Lavoisier, inspired by the ideas of Condorcet, submitted to the Convention a plan for a national system of schools. Primary education was to be free for both sexes “as a duty that society owes to the child.” Secondary education, also open to both sexes, was to be expanded by the establishment of technical colleges throughout France. A month later his rooms were ransacked by governmental agents; among the letters found there, from Lavoisier’s friends, were some that condemned the Revolution and spoke hopefully of foreign armies that would soon overthrow it; other letters showed Lavoisier and his wife planning to escape to Scotland.49 On November 24, 1793, thirty-two former farmers general, including Lavoisier, were arrested. His wife moved every influence to effect his release; she failed, but was allowed to visit him. In prison he continued to work on his exposition of the new chemistry. The financiers were accused of having charged excessive interest, of having adulterated tobacco with water, and of absorbing 130 million livres in illegal profits. On May 5, 1794, they were summoned before the Revolutionary Tribunal. Eight were acquitted; twenty-four, including Lavoisier, were condemned to death. When the presiding judge was asked to commute the sentence on the ground that Lavoisier and some others were savants of value to the state, he was reported to have answered, “The Republic has no need of savants”; but there is no convincing evidence for this tale.50 Lavoisier was guillotined on the very day of the sentence, May 8, 1794, on what is now the Place de la Concorde. Lagrange is said to have commented, “It took only a moment to cut off his head, and a hundred years may not give us another like it.”51

  All the property of Lavoisier and his widow was confiscated to help repay the Republic for the 130,000,000 livres allegedly owed by the ferme générale to the state. Mme. Lavoisier, penniless, was supported by an old servant of the family. In 1795 the French government repudiated the condemnation of Lavoisier; her property was restored to Mme. Lavoisier, who survived till 1836. In October, 1795, the Lycée des Arts held a funeral service in Lavoisier’s memory, with Lagrange delivering the eulogy. A bust was unveiled bearing the inscription “Victim of tyranny, respected friend of the arts, he continues to live; through his genius he still serves humanity.”52

  V. ASTRONOMY

  1. Instrumental Prelude

  How far did the findings of mathematics, physics, and chemistry illuminate the sky? Of all the audacities of science the most daring is the attempt to fling its measuring rods around the stars, to subject those scintillating beauties to nocturnal spying, to analyze their constituents across a billion miles, and to confine their motions to man-made logic and laws. Mind and the heavens are the poles of our wonder and study, and the greatest wonder is mind legislating for the firmament.

  The farseeing instruments had been invented, the major discoveries had been made; the eighteenth century undertook to improve the instruments (Graham, Hadley, Dollond), extend the discoveries (Bradley and Herschel), apply the latest mathematics to the stars (d’Alembert and Clairaut), and organize the results in a new system of cosmic dynamics (Laplace).

  The telescope was bettered and enlarged. “Equatorial telescopes” were made which turned on two axes—one parallel, the other perpendicular, to the plane of the axis of the earth; this choice of axes enabled the observer to keep a celestial object in vie
w long enough for detailed study and micrometric measurement. Newton had been discouraged from use of the refracting telescope by the belief that light, in being refracted by lenses, must necessarily be broken up into colors, so confusing observation; he gave up the problem of making a color-free refraction, and turned to the reflecting telescope. In 1733 Chester Moor Hall, a “gentleman amateur,” solved the problem by combining lenses of different refractive media, neutralizing the diversity of color. He did not publish his discovery, and John Dollond had to work out independently the principles and construction of the achromatic telescope, which he announced in the Philosophical Transactions of the Royal Society of London in 1758.

  In 1725 George Graham, a Quaker watchmaker, made for Edmund Halley at Greenwich Observatory a mural quadrant—a mechanical quarter-circle graduated into degrees and minutes, and fixed on a wall so as to catch the transit of a star across the meridian. For Halley, James Bradley, and Pierre Lemonnier, Graham made transit instruments combining telescope, axis, clock, and chronograph, to mark such transits with greater accuracy than before. In 1730 Thomas Godfrey, a member of Franklin’s intellectual circle in Philadelphia, described to his friends an instrument for measuring angles and altitudes by means of double reflection through opposed mirrors seen in a telescope; but he did not publish it till 1734. In 1730 John Hadley built a similar instrument, an octant—a graduated arc of an eighth of a circle; in 1757 this was enlarged to a sixth. By enabling a navigator to see at once, in the reflecting telescope, both the horizon and the sun (or a star), Hadley’s “sextant” allowed a more precise measurement of the angle separating the objects. This, combined with Harrison’s marine chronometer, made navigation an almost exact science.