Encyclopedia, Difference between revisions of "Hermann von Helmholtz" - New World

From New World Encyclopedia
Line 30: Line 30:
 
}}
 
}}
  
'''Hermann Ludwig Ferdinand von Helmholtz''' (August 31, 1821 &ndash; September 8, 1894) was a [[Germany|German]] [[physician]] and [[physicist]]. In the words of the [[1911 Britannica]], "his life from first to last was one of devotion to science, and he must be accounted, on intellectual grounds, as one of the foremost men of the 19th century." <<'''Better not to use a quote from another encyclopedia here.'''>>
+
'''Hermann Ludwig Ferdinand von Helmholtz''' (August 31, 1821 &ndash; September 8, 1894) was a [[Germany|German]] [[physician]] and physicist who made one of the first formulations of the principle of the conservation of energy. He made important contributions to many fields, including the physiology, mathematics and thermodynamics.
  
 
==Early life==
 
==Early life==
Helmholtz was the son of the [[Potsdam]] Gymnasium headmaster, [[Ferdinand Helmholtz]], who had studied classical [[philology]] and [[philosophy]], and who was a close friend of the publisher and philosopher [[Immanuel Hermann Fichte]]. Helmholtz's work is influenced by the philosophy of [[Johann Gottlieb Fichte|Fichte]] and [[Immanuel Kant|Kant]]. He tried to trace their theories in empirical matters like [[physiology]].
+
Helmholtz was the son of the [[Potsdam]] Gymnasium headmaster, [[Ferdinand Helmholtz]], who had studied classical [[philology]] and [[philosophy]], and who was a close friend of the publisher and philosopher [[Immanuel Hermann Fichte]]. Helmholtz's mother, Caroline Penn was of English extraction.  
  
As a young man, Helmholtz did not distinguish himself in his early studies, but expressed an interest in math and science. At age 17, he expressed an interest in physics, but economic circumstances dictated his career direction as a military doctor. He studied at the medico-surgical institute in Berlin from 1838 to 1842, where he earned his degree upon acceptance of his dissertation on the nerve cells of ganglia. He remained in that city and practiced as an army surgeon, all the while continuing his studies in physics and mathematics in his spare time.
+
As a young man, Helmholtz did not distinguish himself in his early studies, but showed a proficiency in math and science. At age 17, he expressed an interest in physics, but economic circumstances dictated his career direction as a military doctor. He studied at the medico-surgical institute in Berlin from 1838 to 1842, where he earned his degree upon acceptance of his dissertation on the nerve cells of ganglia. He remained in that city and practiced as an army surgeon, all the while continuing his studies in physics and mathematics in his spare time.
  
 
===Conservation of energy===
 
===Conservation of energy===
 
 
His first important scientific achievement, an 1847 [[physics]] treatise on the [[conservation of energy]] was written in the context of his medical studies and philosophical background. He discovered the principle of conservation of energy while studying [[muscle]] [[metabolism]]. He tried to demonstrate that no energy is lost in muscle movement, motivated by the implication that there were no ''vital forces'' necessary to move a muscle.  
 
His first important scientific achievement, an 1847 [[physics]] treatise on the [[conservation of energy]] was written in the context of his medical studies and philosophical background. He discovered the principle of conservation of energy while studying [[muscle]] [[metabolism]]. He tried to demonstrate that no energy is lost in muscle movement, motivated by the implication that there were no ''vital forces'' necessary to move a muscle.  
  
 
Drawing on the earlier work of [[Nicolas Léonard Sadi Carnot|Sadi Carnot]], [[Émile Clapeyron]] and [[James Prescott Joule]], he postulated a relationship between [[mechanics]], [[heat]], [[light]], [[electricity]] and [[magnetism]] by treating them all as manifestations of a single ''force'' ([[energy]] in modern terms<ref>{{Early science terminology warning}}</ref>). He published his theories in his book ''Über die Erhaltung der Kraft'' (''On the Conservation of Force'', 1847).
 
Drawing on the earlier work of [[Nicolas Léonard Sadi Carnot|Sadi Carnot]], [[Émile Clapeyron]] and [[James Prescott Joule]], he postulated a relationship between [[mechanics]], [[heat]], [[light]], [[electricity]] and [[magnetism]] by treating them all as manifestations of a single ''force'' ([[energy]] in modern terms<ref>{{Early science terminology warning}}</ref>). He published his theories in his book ''Über die Erhaltung der Kraft'' (''On the Conservation of Force'', 1847).
  
In 1848 Helmholtz became assistant of the Anatomical Museum in Berlin, and teacher of anatomy at the Academy of Arts. A year later he moved to Konigsberg to assume a professorship in physiology, where he spent the next seven years.  
+
In 1848 Helmholtz became assistant of the Anatomical Museum in Berlin, and teacher of anatomy at the Academy of Arts. A year later he moved to Konigsberg to assume a professorship in physiology, where he spent the next seven years. In 1849, Helmholtz married Olga von Velten.  
 
 
In 1849, Helmholtz married Olga von Velten.  
 
Caroline Penn, mother of helmholtz, family was of English extraction.
 
 
 
  
 
In 1851, Helmholtz revolutionized the field of ophthalmology with the invention of the [[ophthalmoscope]]; an instrument used to examine the inside of the human eye. This made him world famous overnight. Helmholtz's interests at that time were increasingly focused on the physiology of the senses. His main  publication, entitled ''Handbuch der Physiologischen Optik'' (''Handbook of Physiological Optics''), provided empirical theories on spatial vision, [[color vision]], and [[motion perception]], and became the fundamental reference work in his field during the second half of the nineteenth century. His theory of [[accommodation reflex|accommodation]] went unchallenged until the final decade of the twentieth century.
 
In 1851, Helmholtz revolutionized the field of ophthalmology with the invention of the [[ophthalmoscope]]; an instrument used to examine the inside of the human eye. This made him world famous overnight. Helmholtz's interests at that time were increasingly focused on the physiology of the senses. His main  publication, entitled ''Handbuch der Physiologischen Optik'' (''Handbook of Physiological Optics''), provided empirical theories on spatial vision, [[color vision]], and [[motion perception]], and became the fundamental reference work in his field during the second half of the nineteenth century. His theory of [[accommodation reflex|accommodation]] went unchallenged until the final decade of the twentieth century.
  
Helmholtz became professor of anatomy and physiology at the University of Bonn in 1856.  
+
Helmholtz became professor of anatomy and physiology at the University of Bonn in 1856. He became interested in fluid dynamics and showed that movement such as is illustrated by a smoke ring would, in a frictionless fluid, continue forever. This was expanded by William Thomson to a theory of atoms.
 
 
Helmhotz did research on fluid dynamics and showed that movement such as is illustrated by a smoke ring would, in a frictionless fluid, continue forever. This was expanded by William Thomson to a theory of atoms. (1858 Helmholtz study of hydrodynamics.)
 
  
 
In 1859, Helmholtz's first wife died after a long illness; Helholtz and Olga had two children by their marriage. In 1859, he took a position as professor of physiology at the University of Heidelberg. In 1861, Helmholtz married Anna von Mohl, and the couple had two children.
 
In 1859, Helmholtz's first wife died after a long illness; Helholtz and Olga had two children by their marriage. In 1859, he took a position as professor of physiology at the University of Heidelberg. In 1861, Helmholtz married Anna von Mohl, and the couple had two children.
  
In 1871, professor of natural philosophy at the University of Berlin. In 1887, in addition to his teaching duties in Berlin, he became director of the physicotechnical institute in Charlottenburg.
+
==Electromagnetism==
 
 
Helmholtz continued to work for several decades on several editions of the handbook, frequently updating his work because of his dispute with [[Ewald Hering]] who held opposite views on spatial and color vision. Helmholtz tended to rely on experience as an important input to spatial comprehension, while Hering and the so-called "nativists" emphasized the innate intuition has playing the most important role. The philosophical dispute divided the discipline of physiology during the second half of the 1800s.
 
 
 
===Acoustics and aesthetics===
 
 
In 1863 Helmholtz published a book called ''[[On the Sensations of Tone as a Physiological Basis for the Theory of Music]]'', once again demonstrating his interest in the physics of perception. This book influenced musicologists into the twentieth century. Helmholtz invented the [[Helmholtz resonance|Helmholtz resonator]] to show the strength of the various tones.
 
In 1863 Helmholtz published a book called ''[[On the Sensations of Tone as a Physiological Basis for the Theory of Music]]'', once again demonstrating his interest in the physics of perception. This book influenced musicologists into the twentieth century. Helmholtz invented the [[Helmholtz resonance|Helmholtz resonator]] to show the strength of the various tones.
  
==Electromagnetism==
+
In 1871, professor of natural philosophy at the University of Berlin.  
In 1871 Helmholtz moved from [[Heidelberg]] to [[Berlin]] to become a professor in physics. He became interested in [[electromagnetism]].
 
[[Oliver Heaviside]] stated that there were [[longitudinal wave]]s in [[Helmholtz' electromagnetic theory|Helmholtz theory]]. Although he did not make major contributions to this field, his student [[Heinrich Rudolf Hertz]] became famous as the first to demonstrate [[electromagnetic radiation]]. Hertz's discoveries were a direct result of a challenge made to him by Helmholtz to demonstrate the existence of what Maxwell called the displacement current in air or empty space. Helmholtz had predicted E-M radiation from [[Maxwell's equations]], and the [[wave equation]] now carries his name. A large German association of [[research institution]]s, the [[Helmholtz Association]], is named after him.
 
  
 +
In 1871 Helmholtz moved from [[Heidelberg]] to the University of [[Berlin]] where he became a professor of natural philosophy, finally fulfilling his lifelong dream. There he took up some of the problems of electromagnetic theory. His mathematical formulation in this field is known as Helmholtz's equation. Helholtz's student [[Heinrich Rudolf Hertz]] became famous as the first to demonstrate [[electromagnetic radiation]]. Hertz's discoveries were a direct result of a challenge made to him by Helmholtz to demonstrate the existence of what Maxwell had called the displacement current in air or empty space.
  
1882-1883 Introduced concept of free energy, the heat energy available to do work.
+
In 1883 Helmholtz introduced concept of free energy, the heat energy available to do work.
afterwards, monocyclic, thermodynamics, tried to formulate a mechanical basis for science, tried in his last decade to use the principle of least action to unify science.
+
This was an important advance in thermodynamics, and the concept is widely used in thermodynamics today.  
  
 +
In 1887, in addition to his teaching duties in Berlin, he became director of the physicotechnical institute in Charlottenburg. His last years were devoted to an attempt to unify the sciences under the principle of least action.
  
 +
Helmholtz continued to work for several decades on editions of the handbook, frequently updating his work because of his dispute with [[Ewald Hering]] who held opposite views on spatial and color vision. Helmholtz tended to rely on experience as an important input to spatial comprehension, while Hering and the so-called "nativists" emphasized the innate intuition as playing the most important role. The philosophical dispute divided the discipline of physiology during the second half of the 1800s.
  
==Students and associates==
+
==Achievements==
 +
===Students and associates===
 
Other students and research associates of Helmholtz at Berlin included [[Max Planck]], [[Heinrich Kayser]], [[Eugen Goldstein]], [[Wilhelm Wien]], [[Arthur König]], [[Henry Augustus Rowland]], [[A. A. Michelson]], and [[Michael Pupin]].  [[Leo Koenigsberger]], who studied at Berlin while Helmholtz was there, wrote the definitive biography of him in 1902.
 
Other students and research associates of Helmholtz at Berlin included [[Max Planck]], [[Heinrich Kayser]], [[Eugen Goldstein]], [[Wilhelm Wien]], [[Arthur König]], [[Henry Augustus Rowland]], [[A. A. Michelson]], and [[Michael Pupin]].  [[Leo Koenigsberger]], who studied at Berlin while Helmholtz was there, wrote the definitive biography of him in 1902.
  
==Sensory physiology==
+
===Sensory physiology===
 
The sensory physiology of Helmholtz was the basis of the work of [[Wilhelm Wundt]], a student of Helmholtz, who is considered one of the founders of experimental [[psychology]]. He, more explicitly than Helmholtz, described his research as a form of empirical philosophy and as a study of the mind as something separate. Helmholtz had in his early refutal of the speculative early nineteenth century tradition of ''Naturphilosophie'' stressed the importance of [[materialism]], and was focusing more on the unity of "mind" and body.
 
The sensory physiology of Helmholtz was the basis of the work of [[Wilhelm Wundt]], a student of Helmholtz, who is considered one of the founders of experimental [[psychology]]. He, more explicitly than Helmholtz, described his research as a form of empirical philosophy and as a study of the mind as something separate. Helmholtz had in his early refutal of the speculative early nineteenth century tradition of ''Naturphilosophie'' stressed the importance of [[materialism]], and was focusing more on the unity of "mind" and body.
  
 
===Ophthalmic optics===
 
===Ophthalmic optics===
 
 
[[Image:Helmholtz.jpg|thumb|Helmholtz in front of Humboldt University in Berlin]]
 
[[Image:Helmholtz.jpg|thumb|Helmholtz in front of Humboldt University in Berlin]]
 
Helmholtz extended a theory originally proposed by Thomas Young that the human eye detects and is sensitive to only three primary colors. Helmholtz proposed that each of these three colors has a particular type of receptor in the eye that detects it.
 
Helmholtz extended a theory originally proposed by Thomas Young that the human eye detects and is sensitive to only three primary colors. Helmholtz proposed that each of these three colors has a particular type of receptor in the eye that detects it.
  
"...he establishes principles in pure hydrodynamics which have excaped the penetrative power of all the mathematicians who preceded him, including (Joseph Louis) Lagrange himself."Maxwell 597.
+
==Legacy==
 
+
Helmholtz's treatise on the principle of the conservation of energy was widely read and influential. He continued to make major contributions to fields as diverse as physiology, applied mathematics, electromagnetic theory, and thermodynamics. His work, particularly in the philosophy and physiology of perception, continued to exert an influence on scientists through the twentieth century. Said James Clerk Maxwell, "...he establishes principles in pure hydrodynamics which have excaped the penetrative power of all the mathematicians who preceded him, including (Joseph Louis) Lagrange himself. (Maxwell, 597).
Helmholtz emphasized the importance of the interaction of minds in education, particularly of students with professors of great accomplishemnt. When one finds himself in contact with a man of the first order, the entire scale of one's intellectual conceptions is modified for life. Contact with such a man is perhaps the most interesting thing life may have to offer." Johannes Muller Maxwell's papers 753
 
 
 
 
 
1884 monocyclic, thermodynamics, tried to formulate a mechanical basis for science, tried in his last decade to use the principle of least action to unify science.
 
  
Introduced concept of free energy, the heat energy available to do work.
+
he put great stock in the importance of meeting the best minds of his time. "When one finds himself in contact with a man of the first order, the entire scale of one's intellectual conceptions is modified for life. Contact with such a man is perhaps the most interesting thing life may have to offer." (Johannes Muller Maxwell's papers 753)
  
 
==References==
 
==References==
 
* Maxwell, James Clerk. 2003. Hermann Ludwig Ferdinand Helmholtz in ''The Scientific Papers of James Clerk Maxwell'', Mineola, N.Y.: Dover Publications. 1:293. ISBN 0486495604.
 
* Maxwell, James Clerk. 2003. Hermann Ludwig Ferdinand Helmholtz in ''The Scientific Papers of James Clerk Maxwell'', Mineola, N.Y.: Dover Publications. 1:293. ISBN 0486495604.
* Cahan, David. 1993. Hermann von Helmholtz and the foundations of nineteenth-century science. Berkeley: University of California Press. ISBN 0585112894
+
* Cahan, David. 1993. ''Hermann von Helmholtz and the foundations of nineteenth-century science''. Berkeley: University of California Press. ISBN 0585112894
  
 
==Notes==
 
==Notes==

Revision as of 09:54, 9 July 2007

Hermann von Helmholtz

Hermann von Helmholtz.jpg
Hermann Ludwig Ferdinand von Helmholtz
Born

August 31, 1821
Potsdam, Germany

Died September 8, 1894

Charlottenburg, Berlin, Germany

Residence Flag of Germany.svg Germany
Nationality Flag of Germany.svg German
Field Physicist and physiologist
Institutions University of Königsberg
University of Bonn
University of Heidelberg
University of Berlin
Alma mater Royal Friedrich-Wilhelm Institute
Academic advisor  Johannes Peter Müller
Notable students  Albert Abraham Michelson Nobel.svg

Wilhelm Wien Nobel.svg
William James
Heinrich Hertz
Michael Pupin
Friedrich Schottky
Arthur Gordon Webster

Known for Conservation of energy

Hermann Ludwig Ferdinand von Helmholtz (August 31, 1821 – September 8, 1894) was a German physician and physicist who made one of the first formulations of the principle of the conservation of energy. He made important contributions to many fields, including the physiology, mathematics and thermodynamics.

Early life

Helmholtz was the son of the Potsdam Gymnasium headmaster, Ferdinand Helmholtz, who had studied classical philology and philosophy, and who was a close friend of the publisher and philosopher Immanuel Hermann Fichte. Helmholtz's mother, Caroline Penn was of English extraction.

As a young man, Helmholtz did not distinguish himself in his early studies, but showed a proficiency in math and science. At age 17, he expressed an interest in physics, but economic circumstances dictated his career direction as a military doctor. He studied at the medico-surgical institute in Berlin from 1838 to 1842, where he earned his degree upon acceptance of his dissertation on the nerve cells of ganglia. He remained in that city and practiced as an army surgeon, all the while continuing his studies in physics and mathematics in his spare time.

Conservation of energy

His first important scientific achievement, an 1847 physics treatise on the conservation of energy was written in the context of his medical studies and philosophical background. He discovered the principle of conservation of energy while studying muscle metabolism. He tried to demonstrate that no energy is lost in muscle movement, motivated by the implication that there were no vital forces necessary to move a muscle.

Drawing on the earlier work of Sadi Carnot, Émile Clapeyron and James Prescott Joule, he postulated a relationship between mechanics, heat, light, electricity and magnetism by treating them all as manifestations of a single force (energy in modern terms[1]). He published his theories in his book Über die Erhaltung der Kraft (On the Conservation of Force, 1847).

In 1848 Helmholtz became assistant of the Anatomical Museum in Berlin, and teacher of anatomy at the Academy of Arts. A year later he moved to Konigsberg to assume a professorship in physiology, where he spent the next seven years. In 1849, Helmholtz married Olga von Velten.

In 1851, Helmholtz revolutionized the field of ophthalmology with the invention of the ophthalmoscope; an instrument used to examine the inside of the human eye. This made him world famous overnight. Helmholtz's interests at that time were increasingly focused on the physiology of the senses. His main publication, entitled Handbuch der Physiologischen Optik (Handbook of Physiological Optics), provided empirical theories on spatial vision, color vision, and motion perception, and became the fundamental reference work in his field during the second half of the nineteenth century. His theory of accommodation went unchallenged until the final decade of the twentieth century.

Helmholtz became professor of anatomy and physiology at the University of Bonn in 1856. He became interested in fluid dynamics and showed that movement such as is illustrated by a smoke ring would, in a frictionless fluid, continue forever. This was expanded by William Thomson to a theory of atoms.

In 1859, Helmholtz's first wife died after a long illness; Helholtz and Olga had two children by their marriage. In 1859, he took a position as professor of physiology at the University of Heidelberg. In 1861, Helmholtz married Anna von Mohl, and the couple had two children.

Electromagnetism

In 1863 Helmholtz published a book called On the Sensations of Tone as a Physiological Basis for the Theory of Music, once again demonstrating his interest in the physics of perception. This book influenced musicologists into the twentieth century. Helmholtz invented the Helmholtz resonator to show the strength of the various tones.

In 1871, professor of natural philosophy at the University of Berlin.

In 1871 Helmholtz moved from Heidelberg to the University of Berlin where he became a professor of natural philosophy, finally fulfilling his lifelong dream. There he took up some of the problems of electromagnetic theory. His mathematical formulation in this field is known as Helmholtz's equation. Helholtz's student Heinrich Rudolf Hertz became famous as the first to demonstrate electromagnetic radiation. Hertz's discoveries were a direct result of a challenge made to him by Helmholtz to demonstrate the existence of what Maxwell had called the displacement current in air or empty space.

In 1883 Helmholtz introduced concept of free energy, the heat energy available to do work. This was an important advance in thermodynamics, and the concept is widely used in thermodynamics today.

In 1887, in addition to his teaching duties in Berlin, he became director of the physicotechnical institute in Charlottenburg. His last years were devoted to an attempt to unify the sciences under the principle of least action.

Helmholtz continued to work for several decades on editions of the handbook, frequently updating his work because of his dispute with Ewald Hering who held opposite views on spatial and color vision. Helmholtz tended to rely on experience as an important input to spatial comprehension, while Hering and the so-called "nativists" emphasized the innate intuition as playing the most important role. The philosophical dispute divided the discipline of physiology during the second half of the 1800s.

Achievements

Students and associates

Other students and research associates of Helmholtz at Berlin included Max Planck, Heinrich Kayser, Eugen Goldstein, Wilhelm Wien, Arthur König, Henry Augustus Rowland, A. A. Michelson, and Michael Pupin. Leo Koenigsberger, who studied at Berlin while Helmholtz was there, wrote the definitive biography of him in 1902.

Sensory physiology

The sensory physiology of Helmholtz was the basis of the work of Wilhelm Wundt, a student of Helmholtz, who is considered one of the founders of experimental psychology. He, more explicitly than Helmholtz, described his research as a form of empirical philosophy and as a study of the mind as something separate. Helmholtz had in his early refutal of the speculative early nineteenth century tradition of Naturphilosophie stressed the importance of materialism, and was focusing more on the unity of "mind" and body.

Ophthalmic optics

Helmholtz in front of Humboldt University in Berlin

Helmholtz extended a theory originally proposed by Thomas Young that the human eye detects and is sensitive to only three primary colors. Helmholtz proposed that each of these three colors has a particular type of receptor in the eye that detects it.

Legacy

Helmholtz's treatise on the principle of the conservation of energy was widely read and influential. He continued to make major contributions to fields as diverse as physiology, applied mathematics, electromagnetic theory, and thermodynamics. His work, particularly in the philosophy and physiology of perception, continued to exert an influence on scientists through the twentieth century. Said James Clerk Maxwell, "...he establishes principles in pure hydrodynamics which have excaped the penetrative power of all the mathematicians who preceded him, including (Joseph Louis) Lagrange himself. (Maxwell, 597).

he put great stock in the importance of meeting the best minds of his time. "When one finds himself in contact with a man of the first order, the entire scale of one's intellectual conceptions is modified for life. Contact with such a man is perhaps the most interesting thing life may have to offer." (Johannes Muller Maxwell's papers 753)

References
ISBN links support NWE through referral fees

  • Maxwell, James Clerk. 2003. Hermann Ludwig Ferdinand Helmholtz in The Scientific Papers of James Clerk Maxwell, Mineola, N.Y.: Dover Publications. 1:293. ISBN 0486495604.
  • Cahan, David. 1993. Hermann von Helmholtz and the foundations of nineteenth-century science. Berkeley: University of California Press. ISBN 0585112894

Notes

  1. The usage of terms such as work, force, energy, and power in the eighteenth and nineteenth centuries by scientific workers does not necessarily reflect the standardized modern usage.

Bibliography

Primary:

  • 1971. Selected Writings of Hermann von Helmholtz. Kahl, Russell, ed. Wesleyan Uni. Press.
  • 1977. Helmholtz: Epistemological Writings. Cohen, Robert, and Wartofsky, Marx, eds. and trans. Reidel.
  • Ewald, William B., ed., 1996. From Kant to Hilbert: A Source Book in the Foundations of Mathematics, 2 vols. Oxford Uni. Press.
    • 1876. "The origin and meaning of geometrical axioms," 663-88.
    • 1878. "The facts in perception," 698-726.
    • 1887. "Numbering and measuring from an epistemological viewpoint," 727-52.
  • Leo Koenigsberger, translated by Frances A. Welby Hermann von Helmholtz (Dover, 1965)

Secondary:

  • Cahan, D.,1993. Hermann Ludwig Ferdinand von Helmholtz and the Foundations of Nineteenth Century Science, University of California Press.

See also

  • Helmholtz free energy
  • Helmholtz coil which was named in his honor.
  • Helmholtz resonance
  • Helmholtz theorem
  • Helmholtz decomposition
  • Helmholtz equation
  • Young-Helmholtz theory, about the trichromatic colour vision

External links

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

The history of this article since it was imported to New World Encyclopedia:

Note: Some restrictions may apply to use of individual images which are separately licensed.