
Vulcan was a theorized
planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a ...
that some pre-20th century astronomers thought existed in an
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such a ...
between
Mercury and the
Sun. Speculation about, and even purported observations of, intermercurial bodies or planets date back to the beginning of the 17th century. The case for their probable existence was bolstered by the
French
French (french: français(e), link=no) may refer to:
* Something of, from, or related to France
** French language, which originated in France, and its various dialects and accents
** French people, a nation and ethnic group identified with Franc ...
mathematician
A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems.
Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...
Urbain Le Verrier
Urbain Jean Joseph Le Verrier FRS (FOR) HFRSE (; 11 March 1811 – 23 September 1877) was a French astronomer and mathematician who specialized in celestial mechanics and is best known for predicting the existence and position of Neptune using ...
who, by 1859, had confirmed unexplained peculiarities in Mercury's orbit and predicted they had to be the result of gravitational influences of another unknown nearby planet or series of
asteroids
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
. A French amateur astronomer's report that he had observed an object passing in front of the Sun that same year led Le Verrier to announce the long sought after planet, which he gave the name Vulcan, had been discovered at last.
Many searches were conducted for Vulcan over the following decades, but despite several claimed observations, its existence could not be confirmed. The need for the planet as an explanation for Mercury's orbital peculiarities was later rendered unnecessary when
Einstein
Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...
's 1915 theory of
general relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. ...
showed that Mercury's departure from an orbit predicted by
Newtonian Physics
Classical mechanics is a physical theory describing the motion of macroscopic objects, from projectiles to parts of machinery, and astronomical objects, such as spacecraft, planets, stars, and galaxies. For objects governed by class ...
was explained by effects arising from the curvature of spacetime caused by the Sun's mass.
Theories and observations
Celestial bodies interior to the orbit of Mercury had been hypothesized, searched for, and even claim to have been observed, for centuries.
Claims of actually seeing objects passing in front of the Sun included those made by the German astronomer
Christoph Scheiner in 1611 (turned out to be the discovery of
sunspots), British lawyer, writer and amateur astronomer
Capel Lofft observations of 'an opaque body traversing the suns disc' on 6 January 1818, and Bavarian physician and astronomer
Franz von Gruithuisen 26 June 1819 report of seeing "two small spots...on the Sun, round, black and unequal in size".
German astronomer J. W. Pastorff reported many observations, on 23 October 1822, 24 and 25 July 1823, six times in 1834, on 18 October 1836, 1 November 1836 and on 16 February 1837, also claimed to have seen two spots; the larger was 3 arcseconds across, and the smaller 1.25 arcseconds.
Theories that there could be planets orbiting inside Mercury's orbit were put forward by British scientist
Thomas Dick in 1838
and by French physicist, mathematician, and astronomer
Jacques Babinet in 1846 who suggested there may be "incandescent clouds of a planetary kind, circling the Sun" and proposed the name "Vulcan" (after the god
Vulcan from
Roman mythology
Roman mythology is the body of myths of ancient Rome as represented in the literature and visual arts of the Romans. One of a wide variety of genres of Roman folklore, ''Roman mythology'' may also refer to the modern study of these represent ...
) for a planet close to the Sun.
[
As a planet near the Sun would be lost in its glare, several observers mounted systematic searches to try to catch it during "]transit
Transit may refer to:
Arts and entertainment Film
* ''Transit'' (1979 film), a 1979 Israeli film
* ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world
* ''Transit'' (2006 film), a 2006 ...
", i.e. when it passes in front of the Sun's disc. German amateur astronomer Heinrich Schwabe searched unsuccessfully on every clear day from 1826 to 1843 and Yale
Yale University is a private research university in New Haven, Connecticut. Established in 1701 as the Collegiate School, it is the third-oldest institution of higher education in the United States and among the most prestigious in the wo ...
scientist Edward Claudius Herrick conducted observations twice daily starting in 1847, hoping to catch a planet in transit.[ French physician and amateur astronomer Edmond Modeste Lescarbault began searching the Sun's disk in 1853, and more systematically after 1858, with a 3.75 inch (95 mm) ]refractor
A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and ...
in an observatory he set up outside his surgery.[
]
Le Verrier's prediction
In 1840, François Arago
Dominique François Jean Arago ( ca, Domènec Francesc Joan Aragó), known simply as François Arago (; Catalan: ''Francesc Aragó'', ; 26 February 17862 October 1853), was a French mathematician, physicist, astronomer, freemason, supporter of ...
, the director of the Paris Observatory
The Paris Observatory (french: Observatoire de Paris ), a research institution of the Paris Sciences et Lettres University, is the foremost astronomical observatory of France, and one of the largest astronomical centers in the world. Its hist ...
, suggested to mathematician Urbain Le Verrier that he work on the topic of Mercury's orbit around the Sun. The goal of this study was to construct a model based on Sir Isaac Newton
Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a " natural philosopher"), widely recognised as one of the g ...
's laws of motion
In physics, motion is the phenomenon in which an object changes its position with respect to time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed and frame of reference to an observer and mea ...
and gravitation. By 1843, Le Verrier published his provisional theory regarding Mercury's motion, with a detailed presentation published in 1845, which would be tested during a transit of Mercury
frameless, upright=0.5
A transit of Mercury across the Sun takes place when the planet Mercury passes directly between the Sun and a superior planet. During a transit, Mercury appears as a tiny black dot moving across the Sun as the planet o ...
across the face of the Sun in 1848. Predictions from Le Verrier's theory failed to match the observations.[
Despite this, Le Verrier continued his work and, in 1859, published a more thorough study of Mercury's motion. This was based on a series of meridian observations of the planet and 14 transits. This study's rigor meant that some unknown factor would cause any differences from observation. Indeed, some discrepancies remained.][ During Mercury's orbit, its ]perihelion
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion.
General description
There are two apsides in any e ...
advances by a small amount, something called perihelion precession. The observed value exceeds the classical mechanics prediction by the small amount of 43 arcsecond
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
s per century.
Le Verrier postulated that the excess precession could be explained by the presence of some unidentified object or objects inside the orbit of Mercury. He calculated that it was either another Mercury size planet or, since it was unlikely that astronomers were failing to see such a large object, an unknown asteroid belt near the Sun.
The fact that Le Verrier had predicted the existence of the planet Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 time ...
in 1846 using the same techniques lent veracity to his claim.
Claimed discovery
On 22 December 1859, Le Verrier received a letter from Lescarbault, saying that he had seen a transit of the hypothetical planet on March 26 of that year. Le Verrier took the train to the village of Orgères-en-Beauce, some southwest of Paris
Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. ...
, to Lescarbault homemade observatory. Le Verrier arrived unannounced and proceeded to interrogate the man.
Lescarbault described in detail how, on 26 March 1859, he observed a small black dot on the face of the Sun. After some time had passed, he realized that it was moving. He thought it looked similar to the transit of Mercury which he had observed in 1845. He estimated the distance it had already traveled, made some measurements of its position and direction of motion and, using an old clock and a pendulum with which he took his patients' pulses, estimated the total duration of the transit (coming up with 1 hour, 17 minutes, and 9 seconds).
Le Verrier was not happy about Lescarbault's crude equipment but was satisfied the physician had seen the transit of a previously unknown planet. On 2 January 1860 he announced the discovery of the new planet with the proposed name from mythology, "Vulcan", at the meeting of the Académie des Sciences
The French Academy of Sciences (French: ''Académie des sciences'') is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research. It was at the ...
in Paris. Lescarbault, for his part, was awarded the Légion d'honneur
The National Order of the Legion of Honour (french: Ordre national de la Légion d'honneur), formerly the Royal Order of the Legion of Honour ('), is the highest French order of merit, both military and civil. Established in 1802 by Napoleon B ...
and invited to appear before numerous learned societies.
Not everyone accepted the veracity of Lescarbault's "discovery", however. An eminent French astronomer, Emmanuel Liais, who was working for the Brazilian government in Rio de Janeiro
Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the Rio de Janeiro (state), state of the same name, Brazil's List of Brazilian states by population, third-most populous state, and the List of largest citi ...
in 1859, claimed to have been studying the surface of the Sun with a telescope twice as powerful as Lescarbault's at the very moment that Lescarbault said he observed his mysterious transit. Liais, therefore, was "in a condition to deny, in the most positive manner, the passage of a planet over the sun at the time indicated".
Based on Lescarbault's "transit", Le Verrier computed Vulcan's orbit: it supposedly revolved about the Sun in a nearly circular orbit at a distance of The period of revolution was 19 days and 17 hours, and the orbit was inclined to the ecliptic
The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agai ...
by 12 degrees and 10 minutes (an incredible degree of precision). As seen from the Earth, Vulcan's greatest elongation from the Sun was 8 degrees.
Attempts to confirm the discovery
Numerous reports reached Le Verrier from other amateurs who claimed to have seen unexplained transits. Some of these reports referred to observations made many years earlier, and many were not dated, let alone accurately timed. Nevertheless, Le Verrier continued to tinker with Vulcan's orbital parameters as each newly reported sighting reached him. He frequently announced dates of future Vulcan transits. When these failed to materialize, he tinkered with the parameters some more.
Shortly after 08:00 on 29 January 1860, F.A.R. Russell and three other people in London saw an alleged transit of an intra-Mercurial planet. An American observer, Richard Covington, many years later claimed to have seen a well-defined black spot progress across the Sun's disk around 1860 when he was stationed in Washington Territory
The Territory of Washington was an organized incorporated territory of the United States that existed from March 2, 1853, until November 11, 1889, when the territory was admitted to the Union as the State of Washington. It was created from th ...
.
No "observations" of Vulcan were made in 1861. Then, on the morning of 20 March 1862, between 08:00 and 09:00 Greenwich Time, another amateur astronomer, a Mr. Lummis of Manchester, England, saw a transit. His colleague, whom he alerted, also saw the event. Based on these two men's reports, two French astronomers, Benjamin Valz and Rodolphe Radau, independently calculated the object's supposed orbital period, with Valz deriving a figure of 17 days and 13 hours and Radau a figure of 19 days and 22 hours.[
On 8 May 1865 another French astronomer, ]Aristide Coumbary
Jean-Bertrand Aristide (born 15 July 1953) is a Haitian former Salesian priest and politician who became Haiti's first democratically elected president. A proponent of liberation theology, Aristide was appointed to a parish in Port-au-Prince in ...
, observed an unexpected transit from Istanbul
Istanbul ( , ; tr, İstanbul ), formerly known as Constantinople ( grc-gre, Κωνσταντινούπολις; la, Constantinopolis), is the List of largest cities and towns in Turkey, largest city in Turkey, serving as the country's economic, ...
, Turkey
Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...
.
Between 1866 and 1878, no reliable observations of the hypothetical planet were made. Then, during the total solar eclipse of July 29, 1878, two experienced astronomers, Professor James Craig Watson, the director of the Ann Arbor Observatory in Michigan
Michigan () is a U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest, upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the List of U.S. states and ...
, and Lewis Swift, from Rochester, New York
Rochester () is a city in the U.S. state of New York, the seat of Monroe County, and the fourth-most populous in the state after New York City, Buffalo, and Yonkers, with a population of 211,328 at the 2020 United States census. Located i ...
, both claimed to have seen a Vulcan-type planet close to the Sun. Watson, observing from Separation, Wyoming, placed the planet about 2.5 degrees southwest of the Sun and estimated its magnitude at 4.5. Swift, observing the eclipse from a location near Denver, Colorado
Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the United ...
, saw what he took to be an intra-mercurial planet about 3 degrees southwest of the Sun. He estimated its brightness to be the same as that of Theta Cancri, a fifth-magnitude star which was also visible during totality, about six or seven minutes from the "planet". Theta Cancri and the planet were nearly in line with the Sun's centre.
Watson and Swift had reputations as excellent observers. Watson had already discovered more than twenty asteroid
An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic o ...
s, while Swift had several comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or Coma (cometary), coma, and sometimes also a Comet ta ...
s named after him. Both described the colour of their hypothetical intra-mercurial planet as "red". Watson reported that it had a definite disk—unlike stars, which appear in telescopes as mere points of light—and that its phase indicated that it was approaching superior conjunction.
Both Watson and Swift had observed two objects they believed were not known stars, but after Swift corrected an error in his coordinates, none of the coordinates matched each other, nor known stars. The idea that ''four'' objects were observed during the eclipse generated controversy in scientific journals and mockery from Watson's rival C. H. F. Peters
Christian Heinrich Friedrich Peters (September 19, 1813 – July 18, 1890) was a German–American university teacher and astronomer at the Litchfield Observatory of Hamilton College, New York, and a pioneer in the study and visual discovery of ...
. Peters noted that the margin of error in the pencil and cardboard recording device Watson had used was large enough to plausibly include a bright known star. A skeptic of the Vulcan theory, Peters dismissed all the observations as mistaking known stars as planets.
Astronomers continued searching for Vulcan during total solar eclipses in 1883, 1887, 1889, 1900, 1901, 1905, and 1908. Finally, in 1908, W. W. Campbell, Director, and C. D. Perrine
C. or c. may refer to:
* Century, sometimes abbreviated as ''c.'' or ''C.'', a period of 100 years
* Cent (currency), abbreviated ''c.'' or ''¢'', a monetary unit that equals of the basic unit of many currencies
* Caius or Gaius, abbreviated as ...
, Astronomer, of the Lick Observatory, after comprehensive photographic observations at three solar eclipse expeditions in 1901, 1905, and 1908, stated: "In our opinion, the work of the three Crocker Expeditions,...brings the observational side of the intermercurial planet problemfamous for half a centurydefinitely to a close."
Hypothesis disproved
In 1915 Einstein
Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...
's theory of relativity
The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and 1915, respectively. Special relativity applies to all physical phenomena in ...
, an approach to understanding gravity entirely differently from classical mechanics
Classical mechanics is a physical theory describing the motion of macroscopic objects, from projectiles to parts of machinery, and astronomical objects, such as spacecraft, planets, stars, and galaxies. For objects governed by classical ...
, removed the need for Le Verrier's hypothetical planet. It showed that the peculiarities in Mercury's orbit were the results of the curvature of spacetime caused by the mass of the Sun. This added a predicted 0.1 arc-second advance of Mercury's perihelion each orbital revolution, or 43 arc-seconds per century, exactly the observed amount (without any recourse to the existence of a hypothetical Vulcan).[William Sheehan, Richard Baum, Vulcan Chase - The Search for an Inside Planet, Astronomy Magazine, December 1997, page 47] The new theory modified the predicted orbits of all planets, but the magnitude of the differences from Newtonian theory diminishes rapidly as one gets farther from the Sun. Also, Mercury's fairly eccentric orbit makes it much easier to detect the perihelion shift than is the case for the nearly circular orbits of Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
and Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...
. Einstein's theory was empirically verified in the Eddington experiment
The Eddington experiment was an observational test of general relativity, organised by the British astronomers Frank Watson Dyson and Arthur Stanley Eddington in 1919. The observations were of the total solar eclipse of 29 May 1919 and were c ...
during the solar eclipse of May 29, 1919
A total solar eclipse occurred on Thursday, May 29, 1919. With the duration of totality at maximum eclipse of 6 minutes 50.75 seconds, it was the longest solar eclipse since May 27, 1416. A longer total solar eclipse would later occur on June 8, ...
when photographs showed the curvature of spacetime was bending starlight around the Sun. Astronomers generally quickly accepted that a large planet inside the orbit of Mercury could not exist, given the corrected equation of gravity.
Today, the International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...
has reserved the name "Vulcan" for the hypothetical planet, even though it has been ruled out, and also for the Vulcanoids, a hypothetical population of asteroids that may exist inside the orbit of the planet Mercury. Thus far, however, earth- and space-based telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...
s and the NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeedi ...
Parker Solar Probe
The Parker Solar Probe (PSP; previously Solar Probe, Solar Probe Plus or Solar Probe+) is a NASA space probe launched in 2018 with the mission of making observations of the outer corona of the Sun. It will approach to within 9.86 solar radii ...
have detected no such asteroids. While three Atira asteroids
Atira asteroids or Apohele asteroids, also known as interior-Earth objects (IEOs), are asteroids whose orbits are entirely confined within Earth's orbit; that is, their orbit has an aphelion (farthest point from the Sun) smaller than Earth's p ...
have perihelion points within the orbit of Mercury, their aphelia are outside that orbital path, therefore they cannot be defined as 'vulcanoids', which would require wholly intra-mercurian circular orbital trajectories, which none of them possess.
See also
* Fictional planets of the Solar System
The fictional portrayal of the Solar System has often included planets, moons, and other celestial objects which do not actually exist in reality. Some of these objects were, at one time, seriously considered as hypothetical planets which were ei ...
* Hypothetical moon of Mercury
Mercury is the closest planet to the Sun and lacks any natural satellites. An undiscovered moon orbiting the planet was hypothesized to exist in the early 1970s, but it turned out to be misinterpreted data from the star 31 Crateris. Observation of ...
* Nemesis (hypothetical star)
* Planet Nine
Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravitational effects could explain the peculiar clustering of orbits for a group of extreme trans-Neptunian objects (ETNOs), bodies beyond Neptune that orb ...
* Planets beyond Neptune
Following the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century and continued at the start of the 20th with Percival Lowell' ...
* John H. Tice John Hower Tice, known as John H. Tice, (1809-1883) was an American weather forecaster, educator, and author.
Professional life
Weather
Tice was "a student of the phenomena of cyclones, and promulgated the theory that they were entirely different ...
, weather forecaster who based predictions on supposed movements of Vulcan
* Tyche (hypothetical planet)
* Vulcan (''Star Trek'')
* Vulcanoids
The vulcanoids are a hypothetical population of asteroids that orbit the Sun in a dynamically stable zone inside the orbit of the planet Mercury. They are named after the hypothetical planet Vulcan, which was proposed on the basis of irregulariti ...
* Atira asteroids
Atira asteroids or Apohele asteroids, also known as interior-Earth objects (IEOs), are asteroids whose orbits are entirely confined within Earth's orbit; that is, their orbit has an aphelion (farthest point from the Sun) smaller than Earth's p ...
* 2021 PH27
is a near-Earth asteroid of the Atira group. It was discovered by Scott Sheppard using the Dark Energy Survey's DECam imager at NOIRLab's Cerro Tololo Inter-American Observatory on 13 August 2021. has the smallest semi-major axis and shorte ...
, an Atira asteroid with an intra-Mercurian perihelion
* (434326) 2004 JG6
, provisional designation , is an eccentric, sub-kilometer sized asteroid, classified as near-Earth object and potentially hazardous asteroid of the Atira group. It is one of the closest orbiting objects to the Sun. While its perihelion lies wi ...
, an Atira asteroid with an intra-Mercurian perihelion
* 2010 XB11, an Atira asteroid with an intra-Mercurian perihelion
References
Further reading
*
* Originally published a
''The Hunt for Vulcan: ... And How Albert Einstein Destroyed a Planet, Discovered Relativity, and Deciphered the Universe''
* The subject was also featured on an episode of '' Arthur C. Clarke's Mysterious World'' entitled "Strange Skies", originally broadcast on November 18, 1980.
External links
* Asimov, Isaac (1975)
"The Planet That Wasn't"
''The Magazine of Fantasy and Science Fiction
''The Magazine of Fantasy & Science Fiction'' (usually referred to as ''F&SF'') is a U.S. fantasy fiction magazine, fantasy and science fiction magazine first published in 1949 by Mystery House, a subsidiary of Lawrence E. Spivak, Lawrence Spiva ...
''
* Schlyter, Paul (2006).
"Vulcan, the intra-Mercurial planet, 1860–1916, 1971"
''The Nine8 Planets: A Multimedia Tour of the Solar System'' (Appendix 7: "Hypothetical Planets") converted to HTML by Bill Arnett.
*
The Planet Vulcan
, ''Scientific American
''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it i ...
'', 31 August 1878, p. 128, columns 2–3
{{DEFAULTSORT:Vulcan (Hypothetical Planet)
Astronomical hypotheses
General relativity
Hypothetical bodies of the Solar System
Hypothetical planets
Mercury (planet)
Obsolete theories in physics
Solar System dynamic theories
Tests of general relativity
Vulcan (mythology)