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• Born: 27 December 1571
• Birthplace: Weil der Stadt, Württemberg
• Died: 15 November 1630
• Best Known As: The astronomer who explained planetary motion

Johannes Kepler supported the heliocentric theory by Nicolas Copernicus, defending it in his first major work, Mysterium Cosmographicum (1596). In 1601 Kepler became the imperial mathematician to Rudolf II (emperor of the Holy Roman Empire), succeeding Tycho Brahe. Using Brahe's data, between 1609 and 1619 Kepler developed his three laws of planetary motion in Astronomia Nova and Harmonices Mundi. Thanks in part to a telescope he received from Galileo (they knew each other through correspondence only), Kepler also advanced the science of optics. His achievements in astronomy and mathematics shaped our current understanding of the solar system.

Kepler wrote a story, "Somnium," that wasn't published until after his death. In the story a man travels to the moon in a dream. Kepler accurately described the surface of the moon as dust and rocks.

Johannes Kepler

Library of Congress

[b. Württemberg (Germany), December 27, 1571, d. Regensburg, Bavaria (Germany), November 15, 1630]

"Just as the eye was made to see colors, and the ear to hear sounds, so the human mind was made to understand, not whatever you please, but quantity," wrote Kepler. Kepler based his investigations on careful observations and complex mathematics, but always with a mystical bent, perhaps from his work as an astrologer. As Tycho Brahe's assistant and successor, he used Tycho's careful observations to discover the three mathematical laws that describe a planet's orbit, the speed at which it travels, and the time it needs to complete one revolution around the Sun. He proved that Earth and other planets travel in orbits that are ellipses, not circles as had been believed since ancient times. And he showed that the speed of a planet in its orbit is not uniform, but decreases as its distance from the Sun increases, thus overthrowing another long-held belief. Kepler also was a founder of the modern science of optics. He was the first to correctly explain how people see -- he noted that the pupil of the eye functions as a diaphragm and that light rays are focused on the retina. He also explained why eyeglasses help people see better. After Galileo Galilei sent him one of the first telescopes, he explained how the instrument works and improved its design.

(b Weil der Stadt, 27 Dec 1571; d Regensburg, 15 Nov 1630). German scientist and philosopher who wrote on music. Mathematician at the Prague court of Emperor Rudolf II (1601-12), he later settled in Linz where his major contribution to music theory, Harmonices mundi, was completed and published in 1619 . In the first two books he traced the origin of the seven ‘harmonies’ of a string back to archetypes inherent in geometry and God. Book 3 contains a treatise on consonance and dissonance, intervals, modes, melody and notation; book 4 is on astrology. In book 5 Kepler described his harmony of the spheres.

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The German astronomer Johannes Kepler (1571-1630) was one of the chief founders of modern astronomy because of his discovery of three basic laws underlying the motion of planets.

Johannes Kepler was born on Dec. 27, 1571, in the Swabian town of Weil. His father, Heinrich Kepler, was a mercenary; although a Protestant, he enlisted in the troops of the Duke of Alba fighting the Reformed insurgents in the Low Countries. Kepler's grandmother brought him up; for years he was a sickly child. At 13 he was accepted at a theological seminary at Adelberg.

Kepler wanted to become a theologian, and following his graduation from the University of Tübingen, as bachelor of arts in 1591, he enrolled in its theological faculty. But he was also interested in French literature and astronomy. His poor health and proclivity to morbidness singled him out no less than did his precocious advocacy of the doctrine of Copernicus.

It seems that the University of Tübingen gladly presented Kepler for the post of the "mathematician of the province" when request for a candidate came from Graz. He arrived there in April 1594 and set himself to work on one of his duties, the composition of the almanac, in which the main events of the coming year were to be duly predicted. His first almanac was a signal success. The occurrence of two not too unlikely events, an invasion by the Turks and a severe winter, which he had predicted, established his reputation.

Far more important for astronomy was the idea that seized Kepler on July 9, 1595. It appeared to him that the respective radii of the orbits of the planets corresponded to the lengths determined by a specific sequence in which the five regular solids were placed within one another, with a sphere separating each solid from the other. The sphere (orbit) of Saturn enveloped a cube which in turn enveloped another sphere, the orbit of Jupiter. This circumscribed a tetrahedron, a sphere (the orbit of Mars), a dodecahedron, a sphere (the orbit of earth), an icosahedron, a sphere (the orbit of Venus), an octahedron, and the smallest sphere (the orbit of Mercury). The idea was the main theme of his Mysterium cosmographicum (1596).

The next year Kepler married Barbara Muehleck, already twice widowed, "under an ominous sky," according to Kepler's own horoscope. Of their five children only one boy and one girl reached adulthood. It was with reluctance that Kepler, a convinced Copernican, first sought the job of assistant to Tycho Brahe, the astrologer-mathematician of Rudolph II in Prague. He took his new position in 1600. On the death of Tycho the following year, Kepler was appointed his successor.

His Three Laws

Kepler's immediate duty was to prepare for publication Tycho's collection of astronomical studies, Astronomiae instauratae progymnasmata (1601-1602). Kepler fell heir to Tycho's immensely valuable records. Their outstanding feature lay in the precision by which Tycho surpassed all astronomers before him in observing the position of stars and planets. Kepler tried to utilize Tycho's data in support of his own layout of the circular planetary orbits. The facts, that is, Tycho's observations, forced him to make one of the most revolutionary assumptions in the history of astronomy. A difference of 8 minutes of arc between his theory and Tycho's data could be explained only if the orbit of Mars was not circular but elliptical. In a generalized form this meant that the orbits of all planets were elliptical (Kepler's first law). On this basis a proper meaning could be given to another statement of his which he had already made in the same context. It is known as Kepler's second law, according to which the line joining the planet to the sun sweeps over equal areas in equal times in its elliptical orbit.

Kepler published these laws in his lengthy discussion of the orbit of the planet Mars, the Astronomia nova (1609). The two laws were clearly spelled out also in the book's detailed table of contents. Thus they must have struck the eyes of any careful reader sensitive to an astronomical novelty of such major proportion. Still, Galileo failed to take cognizance of them in his printed works, although he could have used them to great advantage to buttress his advocacy of the Copernican system.

The relations between Galileo and Kepler were rather strange. Although Galileo remained distinctly unappreciative of Kepler's achievements, the latter wrote a booklet to celebrate Galileo's Starry Messenger immediately upon its publication in 1610. On the other hand, Kepler argued rather vainly in his Conversation with the Starry Messenger (1610) that in his Astronomiae pars optica (1604), or Optics, which he presented as a commentary to Witelo's 13th-century work, one could find all the principles needed to construct a telescope.

In 1611 came Rudolph's abdication, and Kepler immediately looked for a new job. He obtained in Linz the post of provincial mathematician. By the time he moved to Linz in 1612 with his two children, his wife and his favorite son, Friedrich, were dead. Kepler's 14 years in Linz were marked, as far as his personal life was concerned, with his marriage in 1613 to Suzanna Reuttinger and by his repeated efforts to save his aged mother from being tried as a witch.

As for Kepler the scientist, he published two important works while he was in Linz. One was the Harmonice mundi (1618), in which his third law was announced. According to it the squares of the sidereal periods of any two planets are to each other as the cubes of their mean distances from the sun. The law was, however, derived not from celestial mechanics (Newton's Principia was still 6 decades away) but from Kepler's conviction that nature had to be patterned along quantitative relationships since God created it according to "weight, measure and number." Shortly after his first book appeared, he wrote in a letter: "Since God established everything in the universe along quantitative norms, he endowed man with a mind to comprehend them. For just as the eye is fitted for the perception of colors, the ear for sounds, so is man's mind created not for anything but for the grasping of quantities." In the Harmonice mundi he wrote merely a variation on the same theme as he spoke of geometry which "supplied God with a model for the creation of the world. Geometry was implanted into human nature along with God's image and not through man's visual perception and experience." The second work was the Epitome astronomiae Copernicanae, published in parts between 1618 and 1621. It was the first astronomical treatise in which the doctrine of circles really or hypothetically carrying the various planets was completely abandoned in favor of a physical explanation of planetary motions. It consisted in "magnetic arms" emanating from the sun.

Kepler was already in Ulm, the first stopover of the wanderings of the last 3 years of his life, when his Tabulae Rudolphinae (1628) was published. It not only added the carefully determined position of 223 stars to the 777 contained in Tycho's Astronomiae instauratae progymnasmata but also provided planetary tables which became the standard for the next century. Kepler died on Nov. 15, 1630. He was a unique embodiment of the transition from the old to the new spirit of science.

Further Reading

The standard modern biography of Kepler was written by Max Caspar and was translated and edited by C. Doris Hellmann as Kepler (1959). The section on Kepler in Arthur Koestler's The Sleepwalkers (1959) is also available as a separate volume, The Watershed: A Biography of Johannes Kepler (1960). For a rigorous discussion of Kepler's astronomical theories see Alexander Koyré, The Astronomical Revolution: Copernicus, Kepler, Borelli (1961; trans. 1969).

For more information on Johannes Kepler, visit Britannica.com.

Kepler, Johannes (or Johannes Keppler, 1571-1630) The founder of modern astronomy, Kepler was born near Stuttgart. It was as an assistant to the Danish astronomer Tycho Brahe (1546-1601) that he began his astronomical career, and from Tycho he derived his respect for minute and accurate observation. He said that it was the slight discrepancy between the actual position of Mars and its predicted position (eight minutes of arc) that pointed the road to a complete reformation of astronomy. Kepler himself harboured many Pythagorean, occult, and mystical beliefs, but his laws of planetary motion are the first mathematical, scientific, laws of astronomy of the modern era. They state (i) that the planets travel in elliptical orbits, with one focus of the ellipse being the sun; (ii) that the radius between sun and planet sweeps equal areas in equal times; and (iii) that the squares of the periods of revolution of any two planets are in the same ratio as the cube of their mean distances from the sun.

(yōhä'nəs kĕp'lər) , 1571–1630, German astronomer. From his student days at the Univ. of Tübingen, he was influenced by the Copernican teachings. From 1593 to 1598 he was professor of mathematics at Graz and while there wrote his Mysterium cosmographicum (1596). This work opened the way to friendly intercourse with Galileo and Tycho Brahe, and in 1600 Kepler became Tycho's assistant in his observatory near Prague. On Tycho's death (1601) Kepler succeeded him as court mathematician to Holy Roman Emperor Rudolf II. In 1609 he published the results of Tycho's calculations of the orbit of Mars. In this celebrated work were stated the first two of what became known as Kepler's laws. In 1612, becoming mathematician to the states of Upper Austria, he moved to Linz. He wrote an epitome of the astronomy of Copernicus in 1618, and in 1619 De cometis and Harmonice mundi (in which was announced the third of Kepler's laws). In 1626, Kepler moved to Ulm. After his death his manuscript writings, bought by Catherine II of Russia, were placed in the observatory of Pulkovo.

Bibliography

See biographies by M. Caspar (tr. 1959, repr. 1962) and A. Armitage (1966); A. Beer, ed., Kepler: Four Hundred Years (1974).

Kepler, Johannes (1571–1630), German astronomer and mathematician; discoverer of the laws of planetary motion. Born into the Protestant minority in the free city of Weil der Stadt, within the Lutheran duchy of Württemberg, Kepler's family was poised at the boundary between the aristocracy and the artisan class. His father and brother Heinrich both served as soldiers; his youngest brother worked as a tinsmith. Kepler was educated at religious schools supported by the duke of Württemberg, and at the University of Tübingen. Here he studied with theologians trained by Philipp Melanchthon (1497–1560), the great German religious and educational reformer, and began a lifelong friendship with his mathematics teacher, the Copernican astronomer Michael Mästlin (1550–1631).

Unable to follow a church career because his scruples prevented him from signing the Formula of Concord, Kepler began his professional life as a teacher in the Protestant gymnasium at Graz, in southern Austria. From here he rose to become an imperial courtier, and achieved lasting fame as an innovator in astronomy. Kepler married twice (1597 and 1613). He was a devoted father who suffered deeply at the early deaths of many of his children, and he seems to have used mathematical research as a solace. Kepler's publication of the Mysterium Cosmographicum (1596; The secret of the universe) began a meteoric rise. Compelled to leave Graz with other Protestants in 1598, he attached himself to the court of Emperor Rudolf II (ruled 1576–1612) in Prague, and succeeded Tycho Brahe as imperial mathematician in 1601. Thus, in only three years, Kepler ascended from the position of a provincial schoolteacher to become the astrological and astronomical adviser to the most powerful monarch in the Christian world, although the emperor proved unreliable as a source of financial support. Kepler immediately began to produce a series of major works, especially the Optics (Astronomiae pars Optica, 1604) and the New Astronomy (1609), which extended and refounded their subjects. Other works (1601, 1610) attempted to reform astrology. In 1612, after the forced abdication and death of Rudolf, Kepler left Prague, but retained his title of imperial mathematician under later emperors. From 1612 to 1626 he and his family made their home in Linz, in Upper Austria, although Kepler traveled widely. While in Linz he produced the Epitome of Copernican Astronomy (1618–1621) and the Harmony of the World (1619). The latter precipitated a violent exchange with the English theosophist Robert Fludd (1574–1637), but Kepler declined an invitation to visit England despite his long-standing admiration for King James I (ruled 1603–1625). During this period his mother was accused of witchcraft. Kepler directed the defense that led to her acquittal in 1620–1621. The work that had secured the favor of the imperial house for so long, the Rudolfine Tables, was completed in 1627.

With the increasing violence and disorder of the Thirty Years' War, Kepler again sought the protection of a powerfulpatron, and he became astrological adviser to A. W. E. von Wallenstein, the leading Catholic general, in 1628. His patron's fall from power immediately preceded his own death, at Regensburg, in 1630. In the Mysterium Cosmographicum, Kepler presented the most important defense of Sun-centered astronomy since the appearance of Nicolaus Copernicus's De Revolutionibus Orbium Coelestium in 1543. Uniting ideas from his education in mathematics and religion, Kepler proposed that God had employed each regular geometrical solid exactly once in the plan of the world. Nesting the solids within each other, the orbs defining the limits of the planets' motions could be inscribed between them. The five regular solids provided the spacing between six orbs, explaining both their relative distances and the number of planets (the Earth-Moon system forms one unit). On both counts Kepler's Sun-centered model could be argued to be superior to the Earth-centered Ptolemaic system. But Kepler's defense of Copernicus faced another rival: the newly proposed hybrid system of Tycho Brahe, in which Earth was central and stationary, the Moonand Sunwent aroundthe Earth, butall the other planets circled the Sun.

On arriving in Prague in 1600, Kepler was effectively subordinated to Brahe, who first set him to writing an attack on an earlier imperial mathematician (A Defense of Tycho against Ursus). Although not actually published during Kepler's lifetime, this work gives valuable insights into both the state of astronomy and Kepler's novel methodological ideas. Brahe had presented Kepler to Rudolf II as the man who would distill Brahe's decades of observations into new astronomical tables that would carry the emperor's name. When Brahe died unexpectedly in 1601, the importance of this project helped Kepler to succeed Brahe as imperial mathematician. Kepler used the superlatively accurate and complete observations to show that Brahe's cosmic scheme was untenable, and to replace Copernicus's circle-based models with elliptical orbits.

In 1604 Kepler published an important work on optics, which treated the nature of light and vision, the phenomena of refraction, and the applications of optics in astronomy. During the same period he established that the path of Mars was an ellipse and introduced a new way of calculating the planet's position based on the novel concept of an orbit with the Sun at one focus (a principle now called the first law of planetary motion). He showed that his new approach was superior not only to the models of Ptolemy and Brahe, but also to the original form of Copernicus's system. Also improving on Copernicus, he was able to show that the planes of the planet's orbits intersected in the Sun. He also suggested that the Sun was the origin of a quasi-magnetic force responsible for the planets' motions. Based on these physical ideas, he argued for a connection between the speed of a planet along its path and the area swept out by the line connecting it to the Sun (now called the second, or area, law). He demonstrated this result first for a circular path, then for an ellipse. Although originally presented only for the case of Mars, the elliptical orbit and the mathematical principles governing its motion were intended to extend to all planets, based on universal physical principles. Kepler advertised the new connection between physics and astronomy in his book's title, A New Astronomy, Based on Causes, or Celestial Physics. It appeared in 1609 after a delay caused by Brahe's heirs.

In Prague, Kepler also produced two important works attempting to reform astrology, On More Certain Foundations for Astrology (1601) and Tertius Interveniens (1610; The intermediary third position [between two extremes]). He rejected the traditional astrological machinery of houses, but retained the idea that geometrical configurations of celestial objects influenced human judgment and caused terrestrial weather. Also in 1610 he gave enthusiastic support to Galileo Galilei (in Conversation with the Sidereal Messenger, 1610, and preface to the Dioptrice, 1611), and confirmed the latter's telescopic discovery of the moons of Jupiter.

During his time in Linz, Kepler's two most important productions were the Harmony of the World (1619) and the Epitome of Copernican Astronomy (which appeared in several volumes, 1617–1621). The former attempted a grand synthesis of geometry, harmonics, astrology, and astronomy, and presented the music of the spheres, in the form of tones generated as planets vary in speed throughout their orbits. Here also Kepler stated the third law of planetary motion, connecting the square of the planetary year with the cube of its mean distance. The Epitome of Copernican Astronomy was a systematic presentation of Kepler's version of the Copernican system, intended as a textbook, and as a basis for understanding Kepler's approach in the Rudolfine Tables. Appearing in 1627, the tables successfully predicted that Mercury would pass across the face of the sun in November 1631, showing that Kepler had improved the accuracy of positional calculations by a factor of ten.

Kepler was an innovator where Copernicus was a renovator. Copernicus had re-centered the planetary system, but his calculations of planetary positions took as their geometrical center the mean sun, a constructed point, located elsewhere than the Sun itself. The Sun played no physical role in Copernicus's system and he retained celestial spheres to move the planets. Like Ptolemy, Copernicus continued to use circles carrying circles to predict the positions of planets against the background of fixed stars, and although distances were calculable in his system, they played no role in predicting positions. Kepler introduced the modern form of Copernicanism. His planets moved freely through the heavens, propelled by a force originating in the Sun, along orbits that intersected at the Sun. They obeyed mathematical laws that united physics and astronomy in a new way. Their path through space was an ellipse, not a circle, and their distances and velocities were linked in the second law.

Kepler's insights were not immediately accepted by contemporaries, but they were vindicated by Isaac Newton (1642–1727), who replaced Kepler's solar force with universal gravitation, and demonstrated that the three laws of planetary motion followed from his own more general laws of motion in the case of a planet moving around the Sun. Although the laws of planetary motion became central results of the later mechanical philosophy, Kepler himself was not a mechanical philosopher. Kepler's sun rotates because of an animating spirit; the planet Earth has a spirit that perceives celestial alignments and creates weather; in the 1609 presentation of Kepler's theory, planets are capable of directing their own motion of approach to or recession from the Sun. In his last work, the Somnium, published posthumously in 1634, another kind of spirit narrates the appearance of the heavens as seen from the Moon. In Kepler's cosmos, mathematical regularities are evidence of controlling minds, and the structure of the universe, which Kepler spent his life uncovering, testifies to the architectonic mind of its Creator.

Bibliography

Primary Sources

Kepler, Johannes. Apologia Tychonis contra Nicolaum Raymarum Ursum. Prague, 1600.

——. De Fundamentis Astrologiae Certioribus. Prague, 1601.

——. Dioptrice. Augsburg, 1611. Reprint, Cambridge, U.K., 1962.

——. Epitome of Copernican Astronomy Books IV and V, and Harmony of the World Book V. Translated by C. G. Wallis. New York, 1995. Translation of Epitome Astronomiae Copernicanae (1617–1621).

——. Harmony of the World. Translated by E. J. Aiton, A. M. Duncan, and J. V. Field. Philadelphia, 1993. Translation of Harmonice Mundi (1619).

——. Kepler's Conversation with Galileo's Sidereal Messenger. Translated by E. Rosen. New York, 1965. Translation of Dissertatio cum Nuncio Siderio (1610).

——. Mysterium Cosmographicum: The Secret of the Universe. Translated by A. M. Duncan. Norwalk, Conn., 1981. Translation of Prodromus Dissertationem Cosmographicarum, continens Mysterium Cosmographicum (1596).

——. New Astronomy. Translated by William H. Donahue. Cambridge, U.K., 1992. Translation of Astronomia Nova Aitiologetos, sev Physica Coelestis (1609).

——. Optics: Paralipomena to Witelo and the Optical Part of Astronomy. Translated by William H. Donahue. Santa Fe, N.M., 2000. Translation of Ad Vitellionem Paralipomena, quibus Astronomiae pars Optica Traditur (1604).

——. Somnium. Translated by E. Rosen. Madison, 1967. Translation of Somnium, sive Astronomia Lunaris (1634).

——. Tabulae Rudolfinae. Ulm, 1627.

——. Tertius Interveniens. Frankfurt am Main, 1610.

Secondary Sources

Barker, Peter, and Bernard R. Goldstein. "Theological Foundations of Kepler's Astronomy." Osiris 16 (2001): 88–113. On the religious background of Kepler's thought.

Caspar, Max. Kepler. Translated and edited by C. Doris Hellman. New York, 1993. The most important scholarly biography of Kepler.

Field, J. V. "A Lutheran Astrologer: Johannes Kepler." Archive for History of Exact Sciences 31 (1984): 189–272. Translation, with commentary, of Kepler's On More Certain Foundations of Astrology.

Gingerich, O., and W. Walderman. "Rudolfine Tables: Introduction." Quarterly Journal of the Royal Astronomical Society 13 (1972): 360–373.

Jardine, N. The Birth of History and Philosophy of Science: Kepler's A Defense of Tycho against Ursus with Essays on its Provenance and Significance. Cambridge, U.K., and New York, 1984. Latin and English versions of Apologia Tychonis contra Nicolaum Raymarum Ursum (1600).

Methuen, Charlotte. Kepler's Tübingen: Stimulus to a Theological Mathematics. Aldershot, U.K., and Brookfield, Vt., 1998. Examines the University of Tübingen at the time of Kepler's education. Valuable for translations of primary sources.

Simon, Gérard. Kepler astronome astrologue. Paris, 1979. A balanced presentation of Kepler's work in both astronomy and astrology. Still the best single book on Kepler.

Stephenson, Bruce. The Composition of Kepler's Astronomia Nova. Princeton, 2001. Details Kepler's tribulations on the way to his most important book.

——. Kepler's Physical Astronomy. 2nd ed. Princeton, 1994. Detailed study of the Mysterium Cosmographicum and New Astronomy.

——. The Music of the Heavens: Kepler's Harmonic Astronomy. Princeton, 1994.

Voelkel, James R. Johannes Kepler and the New Astronomy. Oxford and New York, 1999. Brief, accessible, and accurate biography.

—PETER BARKER

(1571-1630)

Famous German mathematician, astronomer, and astrologer. He was born on December 27, 1571, at Weil in Württemberg and educated at a monastic school at Maulbrunn. He attended the University of Tübingen, where he studied philosophy, mathematics, theology, and astronomy. In 1593 he became professor of mathematics and morals at Gratz in Styria, where he also continued his astrological studies. He had an unhappy home life and was somewhat persecuted for his doctrines.

The famous Rudolphine tables, which he prepared with the astronomer Tycho de Brahe, were printed in 1626.

Some of Kepler's writings were influenced by occult and mystical concepts. In his work De Harmonice Mundi (1619) he expounded a system of celestial harmonies. His book Somnium (1634) was an early speculation about life on the moon. A discussion of Kepler's concept of archetypes appears in "The Influence of Archetypal Ideas on the Scientific Theories of Kepler" in the book The Interpretation of Nature and the Psyche, by C.G. Jung and W. Pauli (1955).

The laws of the courses of the planets, deduced by Kepler from observations made by Tycho, and known as "the three laws of Kepler," became the foundation of Newton's discoveries, as well as of the whole modern theory of the planets. His services in the cause of astronomy place him high among the distinguished people of science, and in 1808 a monument was erected to his memory at Ratisbon. Kepler's most important work is his Astronomia nova, seu Physica Coelestis tradita Commentariis de Motibus Stellae Martis (1609), which is still regarded as a classic by astronomers.

Kepler died November 15, 1630, at Ratisbon.

A German astronomer of the late sixteenth and early seventeenth centuries. Kepler's three laws governing the motion of the planets made modern astronomy possible. His first law includes his discovery that the orbits of the planets are ellipses.

IN BRIEF: n. - German astronomer who first stated laws of planetary motion (1571-1630).

Quotes:

"The diversity of the phenomena of nature is so great, and the treasures hidden in the heavens so rich, precisely in order that the human mind shall never be lacking in fresh nourishment."

"Nature uses as little as possible of anything."