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How Should Scientists Deal with Occult Phenomena?


Magnetism and electrostatic forces were regarded as occult action at a distance from ancient times and the inquiry into it waned when Christianity that banned magic had strong power. Since the Renaissance, however, researchers dared to study the occult magic and thus they pioneered modern electromagnetism and mechanics. Newton and Coulomb recognized gravitation and electromagnetism as action at a distance but today they are explained as action through medium. The lesson we must learn from history of electromagnetic theory is that we should not refuse study in occult phenomena because of its occult appearances but, as accepting action at a distance is not science but occultism, it should be explained as action through medium.

Image by loulou Nash + ep793 + OpenClipart-Vectors from Pixabay modified by me

1. How did the Ancients grasp electromagnetism?

The ancient Greek knew that amber, when rubbed, attracts light bodies and magnetic iron ore attracts iron. Diogenēs Laertios (Διογένης Λαέρτιος) wrote in the 3rd century, “Aristotle and Hippias affirm that, arguing from the magnet and from amber, Thales attributed a soul or life even to inanimate objects.[1]" It seems that Thales of Miletus (Θαλῆς; c. 624 BC – c. 546 BC) supposed amber and magnetic iron had such power as a soul or life had to move bodies. The electrostatic force and the magnetic force as actions at a distance were the ground for Greek hylozoism[2].

It is natural to associate the magnetic or electrostatic attraction with human attraction. Chinese called a magnet (磁石) “affection stone (慈石) " before the era of the Han dynasty, because a magnet attracts iron just as the mother’s affection attracts her child[3]. The Sanskrit word for a magnet, “अयस्कान्त (ayaskAnta) “, is literally “iron-lover". The Latin “adamas", the Spanish “imán" and the Portuguese “ímã" derive from a verb meaning “love". In the Medieval Europe it was believed that a wife’s chastity could be tested by placing a magnet against her head while she was lying in bed, because her falling out of bed indicated she was unfaithful and her clinging to her husband proved she was faithful[4]. This superstition is based on the association of attraction/repulsion with human love/hate.

According to Alexander of Aphrodisias (Ἀλέξανδρος ὁ Ἀφροδισιεύς) in about 200 AD, Empedocles (Ἐμπεδοκλῆς; c. 490–430 BC) regarded the electrostatic or magnetic force not as action at a distance but as action through medium.

Empedocles says that the iron is borne towards the stone by the effluvia emanating from both and because the pores of the stone are fitted to receive the effluvium of the iron. The effluvium of the stone then expels the air from the pores of the iron. Once the air is expelled, the iron itself is carried along by the abundant flow of the effluvium. Again, when the effluvium of the iron moves towards the pores of the stone, which are fitted to receive it, the iron begins to move with it.[5]

To be sure, iron filings sprinkled on paper placed above a bar magnet, as the picture below shows, represent a pattern as if the supposed effluvium had moved along it. If the flow of the effluvium causes magnetism, it is no longer necessary to suppose the unidentifiable action at a distance.

The magnetic field represented by the alignment of iron filings.[6]

Is electromagnetism force action at a distance or action through medium? This is the crucial issue in the history of electromagnetic theory from the ancient. It is often said the theory of action through medium is mechanistic and rationalistic while the theory of action at a distance is hylozoic and occult. But Empedocles, the proponent of the former, used such a hylozoic expression as to describe the attraction of different things as Love (φιλία) and their separation as Strife (νεῖκος) . The proponents of the latter after Newton have no hylozoic or occult[7] implication. So, the correspondence has no necessity, though we can find such a tendency before Newton.

Democritus, Epicurus, Lucretius, Diogenes of Apollonia, later Plato, Plutarch succeeded to the theory of Empedocles and early Plato, Aristotle, Galen, Alexander of Aphrodisias carried on the tradition of Thales.[8]. The debate was not settled in antiquity and faded away in the medieval period until it restarted from the Renaissance.

2. How was magic treated after the Middle Ages?

Europe got through the dark ages after the Renaissance of the 12th century. We are apt to think Europe became modern by the separation from magic, but we must notice that magic such as astrology and alchemy that seem to symbolize the medieval dark ages flourished in transition from the medieval period to the modern times and that study in magic contributed to modern science. The table below shows this transition.

The transition from the medieval period to the modern times
PeriodIntellectual PioneerAttitude toward MagicRepresentative Researchers
Early Middle Ages (5-11century)ChurchmenProhibition of magicMarbodus
High Middle Ages (12-13 century)Scholars in universitiesInterpretation of magicThomas Aquinas
Late Middle Ages (14-16 century)Engineers and magiciansExperiment in magicParacelsus, Porta, Gilbert
Early Modern (17-18 century)Members of AcademyScientific rationalization of magicNewton, Coulomb
Modern (19-20 century)University researchersExclusion of magicFaraday, Einstein

In the Middle Ages before the Renaissance of the 12th century the Catholic Church had strong power. Libraries were mostly confined to abbeys and intellectuals to monks. Since the Church prohibited pagan magic, there was no formal study concerning electromagnetism that was associated with magic. As the religious suppression was not so severe as in the early modern age of witch-hunt, informal study of folklore remained such as De Lapidibus by Marbodius of Rennes (c. 1035 – 1123) which wrote practical or medical utilities of magnetism.

The ancient Greek texts preserved and studied in the Islamic world had been transmitted to Western Europe since the 12th century. Universities independent of the Church were established to translate and study the imported documents. The representative scholar of this time was Thomas Aquinas (1225 – 7 March 1274) who synthesized the pagan philosophy of Aristotle and the doctrine of the Bible into a coherent system of scholasticism. He gave an Aristotelian explanation for magnetism saying, “just as the generator of a thing moves heavy and light things inasmuch as it gives them the form through which they are moved to their place, so the magnet confers some quality on the iron by which it is moved toward itself[9]."

After his death scholasticism established by Thomas became a dogma in the university education. “European universities started as associations of students and teachers to absorb the knowledge brought about in the 12th century translation movement, and they were open, dynamic and advanced organizations when established, but already in the 15th century they became closed, aristocratic and conservative ones[10]." The new pioneers of knowledge in the Renaissance were scholars and engineers with no affiliation to the Church or universities. They engaged in the experiment to study magical phenomena instead of the interpretation of texts.

The first example was Petrus Peregrinus (Pierre Pelerin de Maricourt), a French engineer who wrote in 1269 the earliest scientific treatise on the magnet, The letter of Petrus Peregrinus, where he demonstrated by experiment that divided magnets show polarity respectively. The mainstream of the late Renaissance was mysticism influenced by Hermetica, a body of mystical Neo-Platonic texts about alchemy, astrology, magic, theurgy and so on written in Egypt from the 2nd to the 6th century, but believed to be much older during the Renaissance. Marsilio Ficino (Marsilius Ficinus; 19 October 1433 – 1 October 1499) translated Hermetica into Latin and published it in 1471. Then Hermeticism became in fashion in the 16th century and researchers tried to verify it by experiment.

As for electromagnetism Paracelsus (1493 – 1541), Giambattista della Porta (1538 – 1615), William Gilbert (1544 – 1603) are famous. Paracelsus proposed a weapon salve, a remedy for healing a wound caused by a bladed weapon with an ointment applied to the blade of the weapon that caused the wound. Porta wrote a popular book titled Magia Naturalis and pointed out that not only magnetism but also magnetization is action at a distance and the distance diminishes their force. Gilbert distinguished magnetism from electrostatic force for the first time, discovered the earth is a magnet and tried to explain the rotation of the earth by means of the terrestrial magnetism. He, however, still preserved the hylozoic tradition of regarding the earth as a life that had a soul.

At this period Copernicus and Kepler, influenced by Neo-Platonic Hermeticism that worshiped the Sun, proposed the heliocentric model. Kepler succeeded to Gilbert’s theory and identified gravitation with magnetism so as to explain the revolution of the solar system. Of course not all pioneers of the Renaissance science were inspired by Hermeticism and advocated the theory of action at a distance. Galileo and Descartes proposed a mechanistic worldview and refused Aristotelian teleology and hylozoism, admitting only action through medium between inanimate bodies and denying action at a distance. While Kepler ascribed ebb and flow to the gravitation of the sun and the moon, Galileo denied this action at a distance and tried to explain them in terms of the local action, namely the progress and the retrogress of the rotation and revolution of the earth. Descartes considered magnetism to be the circulation of tiny helical particles (particulae striatae) flowing through threaded pores in magnets, as Fig. 2 in Principles of Philosophy shows.

The illustration of the magnetic field of the earth and magnets drawn by René Descartes in 1644.[11]

The mechanistic worldview of Galileo and Descartes might seem modern but their theory of action through medium was wrong. Galileo’s theory could not account for the semidiurnal cycle of ebb and flow and Cartesian theory of the circulation of tiny helical particles was refuted by Robert Boyle’s experiments that vacuum does not weaken magnetism[12].

Yamamoto Yoshitaka, a Japanese historian of science, criticized Descartes as follows.

His physics, especially his cosmology, lacks completely the requisites of modern physics and modern astronomy that should examine by exact measurement the result that is introduced from mathematical inference. He utterly ignored the exact mathematical law of planetary motions discovered by Kepler. He had no idea of quantitative measurement of magnetism and he just made up imagined particles that represented the qualitative behavior of magnetism. In this sense Cartesian mechanistic explanation as a physical theory was an immature and therefore imperfect antithesis of magical thought.[13]

Ironically enough it was not Descartes, the seemingly modern mechanistic philosopher, but Newton, a seemingly pre-modern mystic, occult maniac and alchemist, who distinguished gravity from magnetism and founded modern physics. Ricker says “It is a surprising and curious fact that the belief in the ideas of natural magic and astrology persisted almost up to the end of the seventeenth century[14]" , but it was because they believed in the ideas of natural magic and astrology that Hermetic scientists could study action at a distance as such and Newton could discover the law of gravitation and write the Principia.

3. What was the essence and cause of Newton’s success?

When Newton published Principia (Mathematical Principles of Natural Philosophy) in 1687, followers of Cartesian vortex theory on the European Continent did not accept Newtonian universal gravitation. Leibniz criticized it as “an intelligible occult quality[15]" . In fact the idea that the sun and the moon exert a powerful force on the earth is astrological and accepting action at a distance without knowing its essence and cause seems equal to accepting mysterious magic. But as the mechanistic theory was so barren, Newtonian physics was accepted even on the European Continent.

The decisive evidence was the shape of the Earth. If Cartesian vortex theory is correct, it should be prolate, because the pressure of vortex particles is higher near the equator than near the poles. If Newtonian gravitational theory is correct, the Earth should be prolate, because of the centrifugal force. To settle this dispute, King Louis XV sent the survey teams including Maupertuis to Lapland and Peru to measure the length of a degree of the meridian near arc and equator in 1736. In 1738 Maupertuis concluded that the length near arc is longer thanthat near equator[16] and Newton’s prediction turned out to be correct.

Newtonian success prompted scientists to apply the paradigm to other fields. In 1725 Pieter van Musschenbroek published the result of experiment that denied effluvium is the cause of magnetism. In 1760 Johann Tobias Mayer published Theoria Magnetis and refuted Cartesian vortex theory. He also suggested an inverse-square law of magnetism which Charles-Augustin de Coulomb demonstrated in 1785. Coulomb found a similar law is applicable to electrostatic interaction between electrically charged particles. The law is now called Coulomb’s law. Yamamoto sums up the history of debate between the theory of action at a distance and that of action through medium as follows.

While Newtonian physics was accepted on the Continent, the importance of the law was stressed as to gravitation and physicists no longer pondered philosophical questions about “the essence of gravitation" and “the cause of gravitation". Musschenbroek, Mayer and Coulomb extended this process to electromagnetism. Thus electromagnetic forces were rationalized as action at a distance expressed as mathematical functions and got the status of essential concept in modern physics. Electromagnetics as physics started at this point.

In this way the material world was rationalized and magnetism as action at a distance that had been regarded as typical occult force since the antiquity was stripped of magical character. Even the theological ground that Newton attributed to gravitation is out of the question. Physics abandoned the metaphysical recognition of the essence and was satisfied with mathematical certainty of phenomenal law. Mathematical physics started at this point.[17]

This is a common remark on Newtonian revolution or more generally the modern scientific revolution. Before Newton Galileo propounded a similar theory of knowledge. In our speculating, Galileo wrote, “we either seek to penetrate the true and internal essences of natural substances, or content ourselves with knowledge of some of their properties. The former I hold to be as impossible an undertaking with regard to the closest elemental substances as with more remote celestial things.[18]" He thought all we could do is the apprehension of some properties of things.

Newton’s famous phrase, “hypotheses non fingo (I frame no hypotheses)" seems to be akin to Galileo’s idea[*].

[*] Newton actually ventured hypotheses, but did not publish them for fear that he might get involved in a controversy. Newton thought that the gravity as an action at a distance was irrational and speculated about an aether serving as a medium for the gravitational interactions in a letter to Boyle in 1679[19], although he could have no confidence in this hypothesis. The gravity as an action at a distance was supported by those more Newtonian than Newton such as Daniel Bernoulli.

“Hypotheses non fingo" is found in his essay, “General Scholium", which was appended to the second (1713) edition of the Principia.

I have not been able to discover the cause of those properties of gravity from phaenomena, and I frame no hypotheses; for whatever is not deduced from the phaenomena is to be called an hypothesis; and hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy. In this philosophy particular propositions are inferred from the phenomena, and afterwards rendered general by induction. [20]

Now that our experience is limited, an inductive method cannot give a complete demonstration to any general proposition. Any general proposition deduced from phenomena retains the status of hypothesis. So does Newton’s would-be theory. Newton claimed that his doctrine of light and colors should be a theory, not a hypothesis[21] but he also put forward a corpuscular hypothesis of light at the same time. The absolute space and time that Newton presupposed in the Principia was also a hypothesis that we no longer support. Scientists should not be inhibited from advancing hypotheses. Otherwise science could never make progress, because the progress of science is nothing but modification of hypotheses.

So it is not a right remark that Newton’s thesis, “hypotheses non fingo" became the paradigmatic methodology of modern science. Neither is it right to regard the questions about the essence or the cause of action at a distance as “metaphysical recognition" and be satisfied only with superficial description of phenomena. The inquiry into the essence and the cause of phenomena is also necessary for positive science. It is inappropriate to attribute the essence and cause of Newton’s success to him giving up attributing gravitation to its essence and cause. Yamamoto’s conclusion might produce an impression that the theory of action at a distance finally beat the theory of action through medium, but after Newton and Coulomb scientists have conducted an inquiry into the essence and the cause of electromagnetism and now the mainstream of today’s theory consider it to be action through medium. Therefore Descartes was not as reactionary as Yamamoto asserted. Of course we can say his theory lacks qualitative analysis but the same thing holds true for the pioneers of the theory of action at a distance.

The first scientist who revived the theory of action through medium was Faraday (Michael Faraday; 1791 – 1867). Faraday assumed invisible medium even in a vacuum that would transmit the Coulomb force. His idea is akin to Cartesian model that assumed aether composed of invisible “subtle materials[22]" that filled space and transmitted light. Although Michelson-Morley experiment refuted aether as medium of electromagnetism in 1887, the experiment by Heinrich Rudolf Hertz (1857 – 1894) in 1888 demonstrated the existence of electromagnetic wave and the theory of action through medium proved true. Physicists now consider the medium of electromagnetism not as materials that fill the space but the space (field) itself. According to the quantum theory a vacuum is not really vacant but a fluctuating field of continuously appearing and disappearing virtual pairs of particles that can transmit electromagnetic wave.

Quantum field theory does not cover gravitation but according to the general theory of relativity gravity is a phenomenon resulting from the curvature of spacetime. Massive bodies attract each other by distorting spacetime via their mass rather than by action at a distance. Just as change in electromagnetic field propagates as an electromagnetic wave and exerts electromagnetism, change in gravitational field propagates as a gravitational wave and exerts gravity. In 1974 the precision measurements of the slow orbital inspiral of the Hulse-Taylor binary pulsar indirectly proved the existence of gravitational waves and various gravitational wave detectors are not trying direct measurement. Gravitation and electromagnetism that were once thought to be occult actions at a distance are now explained as action through medium. The superstring theory is elucidating the essence of the force. The inquiry into the essence and the cause of phenomena is producing a result.

4. How should scientists deal with occult phenomena?

In the 17-18th century when Newton and Coulomb made a scientific elucidation of action at a distance, not all eminent scientists were university professors. Newton was the Lucasian Professor of Mathematics at the University of Cambridge when he was young, but Coulomb was an engineer in no affiliation with universities. A university was just an educational organization and it was not rare that a researcher who did not belong to a university became an important member of an academy. It was not until the 19th century that a university functioned as a research institute as well in Germany. This tendency spread all over the world in the 20th century. Today the Government offers huge taxpayers’ money to universities and thanks to it scientists in them can conduct an expensive experiment. As a result most of eminent scientists belong to universities.

The current university researchers no longer engage in occult study as scientists in the Renaissance did. It seems quite reasonable that a researcher who receives a research subsidy should not be concerned with occult phenomena, but there can be another way of thinking. Since taxpayers finance researchers, they should not refuse to conduct research that can answer the questions that taxpayers are interested in. Occultism is not out of fashion. Many people are still interested in occult phenomena such as divination, astrology, spiritualism, extra-sensory perception and other paranormal subjects. That is why many commercial media still deal with them.

While the commercial media give an entertaining treatment of occultism, academic researchers contemptuously ignore it. Looking back upon the history of electromagnetism, I wonder whether this is a desirable situation. The Church oppressed pagan thought in the past. For example, the Catholic Church executed Giordano Bruno (1548 – 1600), a Renaissance Hermeticist, owing to heterodoxy. Such an oppression of pagan thought is based on prejudice and has no rational reason. The Renaissance researchers could found modern physics and electromagnetics because they were free from the prejudice that action at a distance was magic, occult and therefore pagan.

Even today study in seemingly occult phenomena might lead to a new science. Although most of occult phenomena that commercial media take up are the result of misidentification and fabrication, still some remain unaccountable. If they turn out to be facts, scientists must explain the phenomena, however strange it may appear, because the role of scientists is explain the given fact rationally and they do not have any right to deny the fact itself.

William Stanley Jevons (1835 – 1882) pointed out the correlation between business cycle and the sunspot number in 1878[23], but his suggestion that the sun would influence human economy is so occult and astrological an idea that professional economists have neglected this hypothesis. Certainly accepting the sun’s unidentifiable action at a distance as such is occult and not scientific, but if you can find its essence and cause that make it an action through medium, financial astrology can be scientific financial astronomy, so it is not scientific to refuse it as pseudoscience from the beginning. The same thing holds true of more mysterious phenomena. A mystic who believes in mystery as such and a scientist who refuse to study mysterious phenomena because of its mysterious appearances seem opposite but in truth they are the same in that they consider mystery to be mysterious. What scientists should do is to make mystery not mysterious.

5. References

  1. “Ἀριστοτέλης δὲ καὶ Ἱππίας φασὶν αὐτὸν καὶ τοῖς ἀψύχοις μεταδιδόναι ψυχάς, τεκμαιρόμενον ἐκ τῆς λίθου τῆς μαγνήτιδος καὶ τοῦ ἠλέκτρου." Διογένης Λαέρτιος. Βίοι καὶ γνῶμαι τῶν ἐν φιλοσοφίᾳ εὐδοκιμησάντων.Θαλής, 23.
  2. Hylozoism derives from Greek ὕλη meaning “matter" and ζωή meaning “life". It is a doctrine held especially by early Greek philosophers that all matter has life. Here I use this term in a wide sense including modern vitalism.
  3. “磁石召鐵,或引之也. 石,鐵之母也. 石之不磁者,亦不能引之也." 李昉, 徐鉉 et al. 『太平御覽』藥部五, 石藥下. Chinese Text Project.
  4. Pedanius Dioscorides. De Materia Medica. Vol.5, §.148.
  5. Empedoklēs. Supplementum Aristotelicum vol. 2, pars 1-2. Alexandri Aphrodisiensis praeter commentaria scripta minora. 2. Quaestiones. De fato. De mixtione. edidit Ivo Brun. Ulan Press (August 31, 2012). p. 72 ed. Ivo Brun.
  6. Newton Henry Black, Harvey N. Davis. Practical physics for secondary schools: fundamental principles and applications to daily life.The Macmillan company (1913).
  7. The word “occult" comes from the Latin word “occultus" which means “hidden" and “secret" in opposition to “manifestus" which means “plain" and “evident". It did not necessarily mean “mysterious", but here I use this word in a today’s sense. That is to say an occult force is the action that not only I cannot optically see but also I cannot theoretically see.
  8. 山本義隆. 『磁力と重力の発見〈1〉古代・中世』 みすず書房 (May 23, 2003). p. 91.
  9. “enim generans movet gravia et levia, inquantum dat eis formam per quam moventur ad locum, ita et magnes dat aliquam qualitatem ferro, per quam movetur ad ipsum." Thomas Aquinas. Sancti Commentaria in Octo Libros Physicorum Aristotelis. Thomae Aquinatis Doctoris Angelici Opera Omnia, Vol. 2. Lib. 7. Lec. 3. §. 903.
  10. “ヨーロッパの大学は、12世紀の大翻訳運動によってもたらされた知識の吸収のための教師と学生の組合として始まり、創立当初は開放的で動的で前進的な組織であったが、既に15世紀には閉鎖的で貴族的で守旧的な組織に変質していた" 山本義隆.『磁力と重力の発見〈2〉ルネサンス』みすず書房 (May 23, 2003). p. 439.
  11. René Descartes. Principia Philosophiae. First published 1644. Reprinted: Kessinger Publishing, LLC (August 10, 2009).
  12. Robert Boyle. New experiments, physico-mechanical, touching the spring and weight of the air, and their effects. 1682. Reprinted: EEBO Editions, ProQuest (December 13, 2010).
  13. “彼の自然学、とりわけその宇宙論は、数学的推論によって導かれる結果を精密な測定によって検証するという近代物理学や近代天文学の基本的要件をまったく欠落させている。惑星運動についてのケプラーの精密な数学的法則にいたっては一顧だにされていない。磁力についても、磁力を定量的に測定するという発想はデカルトには皆無で、磁石の定性的なふるまいを再現するモデルを仮想の物質で担造することでその磁力論は尽きている。その意味では、デカルト機械論は、自然学としては、魔術思想に対置された未成熟でそれゆえきわめて不完全なアンチテーゼであったと言わざるをえない。山本義隆. 『磁力と重力の発見〈3〉近代の始まり』みすず書房 (May 23, 2003). p. 765.
  14. H.H. Ricker III. “Magnetism During the 17th Century." The General Science Journals.
  15. “une qualité occulte déraisonnable" Gottfried Wilhelm von Leibniz. Die philosophischen Schriften: Band III. Adamant Media Corporation (March 4, 2002). p. 519.
  16. Pierre Louis Moreau de Maupertuis. La Figure de La Terre. Reprinted: Wentworth Press (July 28, 2018).
  17. “一八世紀にニュートンの力学が大陸に浸透してゆく過程で、重力についてはその「法則」の確定こそが大切であるということが次第に認められてゆき、「重力の本質」や「重力の原因」を問うといったそれまでの哲学での問いは、物理学では主要な問題ではなくなっていった。ミュッセンブルークからマイヤーとクーロンにまでいたる研究はこの過程を電磁力にまで押し広げるものであった。こうして磁気と電気の力もまた、数学的関数で表される遠隔力として合理化されたことで数理物理学にとって不可欠な概念の地位を獲得し、近代物理学に組み込まれていったのである。物理学としての電磁気学はここから始まる。かくして物質的世界は合理化され、遠隔作用として古代以来「隠れた力」の典型と見なされてきた磁力からはその魔術的性格が脱色されていった。もはやニュートンが重力にたいして考えていたような神学的根拠すら語られていない。物理学は事物の本質についての形而上学的な認識を求めることを放棄し、さしあたって現象の法則についての数学的な確実性を求めることに自足したのである。そしてここに数理物理学がはじまる。" 山本義隆. 『磁力と重力の発見〈3〉近代の始まり』みすず書房 (May 23, 2003). p. 935.
  18. Galileo Galilei (Author), Stillman Drake (Translator). Discoveries and Opinions of Galileo. Anchor; 24th edition (March 1, 1957). p. 123.
  19. Newton’s 1679 Letter to Boyle, on the Cosmic Ether of Space." in William Vernon Harcourt. Letter to Henry Lord Brougham. BiblioBazaar (November 11, 2009).
  20. “Rationem vero harum gravitatis proprietatum ex phænomenis nondum potui deducere, et hypotheses non fingo. Quicquid enim ex phænomenis non deducitur, hypothesis vocanda est; et hypotheses seu metaphysicae, seu physicae, seu qualitatum occultarum, seu mechanicae, in philosophia experimentali locum non habent. In hac philosophia Propositiones deducuntur ex phaenomenis, et redduntur generales per inductionem." Isaac Newton. Philosophiae Naturalis Principia Mathematica. General Scholium. 2nd. ed. 1713. Reprinted: PenguinO PS (March 6, 2012).
  21. Newton, Isaac. “A letter of Mr. Isaac Newton, professor of the mathematicks in the University of Cambridge; containing his new theory about light and colors: Sent by the Author to the Publisher from Cambridge, Febr. 6. 1671/72; In Order to be Communicated to the R. Society." Philosophical Transactions of the Royal Society of London. 6.80 (2014): 3075-3087.
  22. “matière subtile" René Descartes. La dioptrique. Complétant le Discours de la méthode de 1637. p. 9.
  23. Jevons, W. Stanley. “Commercial crises and sun-spots." Nature. 19, no. 472 (November 1878): 33–37.