Otto von Guericke

Otto von Guericke was born to a patrician family of Magdeburg.[5] He was privately tutored until the age of fifteen.[6] In 1617 he began studying law and philosophy at the Leipzig University.[3] However, in 1620 his studies at Leipzig were disrupted by his father's death. He briefly returned home before continuing his studies at the Academia Julia in Helmstedt and the universities of Jena and Leiden.[3] It was at Leyden that he first began attending courses on mathematics, physics, and fortification engineering. His education was completed by a nine-month Grand Tour to France and England.[3]

On his return to Magdeburg in 1626 he married Margarethe Alemann. Before Margarethe's death in 1645, they had three children together: Anna Catherine, Hans Otto, and Jacob Christopher.[7] Anna Catherine and Jacob Christopher both died in infancy.[7] Von Guericke later remarried to Dorotha Lentke in 1652.

Von Guericke's political career began upon his return to Magdeburg in 1626.[3] He and his family were educated and well-known; his father and his grandfather had been mayor of the city, which led to von Guericke being appointed an Alderman of Magdeburg.[8]^:213 He was forced to flee Magdeburg during the Holy Roman Empire's brutal sack of the city during the Thirty Years' War, in which four-fifths of the city's population perished. This attack destroyed most of the city as well as von Guericke's personal wealth. Von Guericke returned to Magdeburg in 1631 and, because of his engineering background, led the rebuilding process of the town.[3]

After this rebuilding, he became a master brewer to rebuild his and the town's wealth.[3] In 1646, he was elected as Magdeburg's Burgomeister, a position similar to that of mayor. He remained in this position for more than thirty years until his retirement from office in 1678, after much pressure from younger politicians.[3] During his time in office he went on many diplomatic missions and met with many kings and emperors.[3] In 1666 Otto von Guericke was given aristocratic status by Emperor Leopold I, giving the "von" title to his name and changing the spelling of his last name from "Gericke" to "Guericke".[3]

Otto von Guericke used both his political status and scientific knowledge in tandem to make political gains for his town.[9] His demonstrations of his inventions, such as the air pump and electrostatic generator, were used to impress his audiences and allow for political communications to unfold.[9] He often would not explain scientifically how his shows worked leading people to believe in his wizardry, promoting his status as a great leader.[9] His first diplomatic mission on behalf of the city, in September 1642, was to the court of the Elector of Saxony at Dresden to seek some mitigation of the harshness with which the Saxon military commander treated Magdeburg. In 1648 he represented the city at the treaty delegations following the end of the Thirty Year's War.[8] During another diplomatic mission to Ratisbon in 1654, Guericke used his invention of the air pump to impress those he was meeting and help sway the meeting in his favor, as well as promote his own scientific advancements.[8]^:213 Diplomatic missions, often dangerous as well as tedious, occupied much of his time for the next twenty years. A private scientific life, of which much remains unclear, was developing in parallel.

Inspired by Copernican cosmology and the idea of vast, endless, empty space where light could propagate, bodies could move about unhindered, and sound cannot be detected, von Guericke set about replicating this phenomena on Earth.[8]^:214–15 Von Guericke first started investigating the concept of a vacuum through the use of fire pumps by pumping water out of wooden barrels.[5] However, he soon realised that the porosity of wood was allowing unwanted water, filled with dissolved air, to enter. The pressure fluctuations experienced inside the barrel were allowing this encapsulated air to escape: spoiling the vacuum inside.[5] In 1647 he turned his focus to pumping out enclosed air instead of water to solve this problem.[5]

Portrait of Otto von Guericke by Anselm van Hulle (at the Gripsholm Castle)

His scientific and diplomatic pursuits finally intersected when, at the Reichstag in Ratisbon in 1654, he was invited to demonstrate his experiments on the vacuum before the highest dignitaries of the Holy Roman Empire. One of them, the Archbishop Elector Johann Philip von Schonborn, bought von Guericke's apparatus from him and had it sent to his Jesuit College at Wurzburg. One of the professors at the College, Fr. Gaspar Schott, entered into friendly correspondence with von Guericke and thus it was that, at the age of 55, von Guericke's work was first published as an Appendix to a book by Fr. Schott – Mechanica Hydraulico-pneumatica – published in 1657.[10] This book came to the attention of Robert Boyle who, stimulated by it, embarked on his own experiments on air pressure and the vacuum, and in 1660 published New Experiments Physico-Mechanical touching the Spring of Air and its Effects. The following year this was translated into Latin and, made aware of it in correspondence with Fr. Schott, von Guericke acquired a copy.

In the decade following the first publication of his own work von Guericke, in addition to his diplomatic and administrative commitments, was scientifically very active. He embarked upon his magnum opus — Ottonis de Guericke Experimenta Nova (ut vocantur) Magdeburgica de Vacuo Spatio — which as well as a detailed account of his experiments on the vacuum, contains his pioneering electrostatic experiments in which electrostatic repulsion was demonstrated for the first time and sets out his theologically based view of the nature of space,[11] but there are also contemporary arguments that he did not conceptualise these demonstrations as electrical.[12] In the Preface to the Reader he claims to have finished the book on March 14, 1663 though publication was delayed for another nine years until 1672. In 1664, his work again appeared in print, again through the good offices of Fr. Schott, the first section of whose book Technica Curiosa, entitled Mirabilia Magdeburgica, was dedicated to von Guericke's work. The earliest reference to the celebrated Magdeburg hemispheres experiment is on p. 39 of the Technica Curiosa, where Fr. Schott notes that von Guericke had mentioned them in a letter of July 22, 1656. Fr. Schott goes on to quote a subsequent letter of von Guericke of August 4, 1657 in which he states that he now had carried out the experiment, at considerable cost, with 12 horses.

The 1660s saw the final collapse of Magdeburg's aim, to which von Guericke had devoted some twenty years of diplomatic effort, of achieving the status of a Free City within the Holy Roman Empire. On behalf of Magdeburg, he was the first signatory to the Treaty of Klosterberg (1666) whereby Magdeburg accepted a garrison of Brandenburg troops and the obligation to pay dues to the Great Elector, Friedrich Wilhelm I of Brandenburg. Despite the Elector's crushing of Magdeburg's political aspirations, the personal relationship of von Guericke and Friedrich Wilhelm remained warm. The Great Elector was a patron of scientific scholarship; he had employed von Guericke's son, Hans Otto, as his Resident in Hamburg and in 1666 had named Otto himself to the Brandenburg Rat. When the Experimenta Nova finally appeared it was prefaced with a fulsome dedication to Friedrich Wilhelm.

In 1677 von Guericke, after repeated requests, was reluctantly permitted to step down from his civic responsibilities. In January 1681, as a precaution against an outbreak of plague then affecting Magdeburg, he and his second wife Dorothea moved to the home of his son Hans Otto in Hamburg. There he died peacefully on May 11 (Julian) 1686, 55 years to the day after he had fled the flames in 1631. His body was returned to Magdeburg for interment in the Ulrichskirche on May 23 (Julian) (Schneider p. 144). The Otto von Guericke University Magdeburg is named after him.

There are only three important contemporary sources describing von Guericke's scientific work – Fr. Schott's Mechanica Hydraulico-pneumatica and Technica Curiosa of 1657 and 1664 and his own Experimenta Nova of 1672. His scientific concerns may be divided into three areas, to each of which a Book of the Experimenta Nova is dedicated as follows:

• Book II: the nature of space and the possibility of the void
• Book III: the experimental work on the production of vacua, the pressure of air and the Earth's atmosphere
• Book IV: the investigation into cosmic potencies.

Book II of the Experimenta Nova is an extended philosophical essay in which von Guericke puts forward a view of the nature of space similar to that later espoused by Newton. He is explicitly critical of the plenist views of Aristotle and of their adoption by his younger contemporary Descartes. A particular and repeated target of his criticism is the manner in which the "nature abhors a vacuum" principle had migrated from simply a matter of experiment to a high principle of physics which could be invoked to explain phenomena such as suction but which itself was above question. In setting out his own view, von Guericke, while acknowledging the influence of previous philosophers such as Lessius (but not Gassendi), makes it clear that he considers his thinking on this topic to be original and new. There is no evidence that von Guericke was aware of the Nouvelles Experiences touchant le vide of Blaise Pascal published in 1647. In the Experimenta Nova, Book III, Ch. 34, he relates how he first became aware of Torricelli's mercury tube experiment from Valerianus Magnus at Regensburg in 1654. Pascal's work built upon reports of the mercury tube experiment which had reached Paris via Marin Mersenne in 1644. An indication of the unresolved status of the "nature abhors a vacuum" principle at that time may be taken from Pascal's opinion, expressed in the conclusion of the Nouvelles Experiences, when he writes: "I hold for true the maxims set out below: (a) that all bodies possess a repugnance to being separated one from another and from admitting a vacuum in the interval between them – that is to say that nature abhors a void." Pascal goes on to claim that this abhorrence of a void is however a limited force and thus that the creation of a vacuum is possible.

There were three broad currents of opinion from which von Guericke dissented. Firstly, there was the Aristotelian view that there simply was no void and that everything that exists objectively is in the category of substance. The general plenist position lost credibility in the 17th century, owing primarily to the success of Newtonian mechanics. It was revived again in the 19th century as a theory of an all pervading aether and again lost plausibility with the success of Special Relativity. Secondly, there was the Augustinian position of an intimate relation between space, time, and matter; all three, according to St. Augustine in the Confessions (Ch. XI) and the City of God (Book XI, Ch. VI), came into being as a unity and ways of speaking that purport to separate them – such as "outside the universe" or "before the beginning of the universe" are, in fact, meaningless. Augustine's way of thinking is also attractive to many and seems to have a strong resonance with General Relativity. The third view, which von Guericke discusses at length, but does not attribute to any individual, is that space is a creation of the human imagination. Thus, it is not truly objective in the sense in which matter is objective. The later theories of Leibniz and Kant seem inspired by this general outlook, but the denial of the objectivity of space has not been scientifically fruitful.

Von Guericke sidestepped the vexed question of the meaning of "nothing" by asserting that all objective reality fell into one of two categories – the created and the uncreated. Space and time were objectively real but were uncreated, whereas matter was created. In this way he created a new fundamental category alongside Aristotle's category of substance, that of the uncreated. His understanding of space is theological and similar to that expressed by Newton in the General Scholium to the Principia. For instance, von Guericke writes (Book II, Chapter VII): "For God cannot be contained in any location, nor in any vacuum, nor in any space, for He Himself is, of His nature, location and vacuum."

In 1654 von Guericke invented a vacuum pump consisting of a piston and an air gun cylinder with two-way flaps designed to pull air out of whatever vessel it was connected to, and used it to investigate the properties of the vacuum in many experiments. This pump is described in Chapters II and III of Book III of the Experimenta Nova and in the Mechanica Hydraulico-pneumatica (p. 445-6). Guericke demonstrated the force of air pressure with dramatic experiments.

In 1657, he machined two 20-inch diameter hemispheres and pumped all the air out of them, locking them together with a vacuum seal. The air pressure outside held the halves together so tightly that sixteen horses, eight harnessed to each side of the globe, could not pull the halves apart. It would have required more than 4,000 pounds of force to separate them.[13] It is estimated that by pumping the air out of these spheres, he was able to create internal pressures roughly equal to 1/25 of an atmosphere.[5]

With his experiments Guericke disproved the hypothesis of "horror vacui", that nature abhors a vacuum. Aristotle (e.g. in Physics IV 6–9) had argued against the existence of the void and his views commanded near universal endorsement by philosophers and scientists up to the 17th century. Guericke showed that substances were not pulled by a vacuum, but were pushed by the pressure of the surrounding fluids.

All of von Guericke's work on the vacuum and air pressure is described in Book III of the Experimenta Nova (1672). As regards the more detailed chronology of his work we have, in addition to the Experimenta Nova's description of his demonstrations at Regensburg in 1654, the two accounts published by Fr. Schott in 1657 and 1663.

In Chapter 27 he alludes to what transpired at Regensburg in 1654. The first experiment he explicitly records as having been demonstrated was the crushing of a non-spherical vessel as the air was withdrawn from it. He did not use a vacuum pump directly on the vessel, but allowed the air in it to expand into a previously evacuated receiver.

Engraving by Caspar Schott

The second was an experiment in which a number of men proved able to pull an airtight piston only about halfway up a cylindrical copper vessel. Von Guericke then attached his evacuated receiver to the space below the piston and succeeded in drawing the piston back down again against the force of the men pulling it up. In a letter to Fr. Schott of June 1656, reproduced in Mechanica Hydraulico-pneumatica (p. 454–455), von Guericke gives a short account of his experiences at Regensburg. Based on this, Schimank [1936] gives a list of ten experiments which he considers likely to have been carried out at Regensburg. In addition to the above two, these included the extraction of air using a vacuum pump, the extinction of a flame in a sealed vessel, the raising of water by suction, a demonstration that air has weight, and a demonstration of how fog and mist can be produced in a sealed vessel. The Mechanica Hydraulico-pneumatica also provides the earliest drawing of von Guericke's vacuum pump. This corresponds to the description in the opening chapters of Book III of the Experimenta Nova of the first version of his pump.

Stimulated by the interest taken in his work, von Guericke was scientifically very active in the decade after 1654. In June 1656 we find him writing to Fr. Schott (Mechanica Hydraulico-pneumatica, p. 444) "Since the time when I produced the exhibition for the said eminent Elector, I have a better and clearer grasp of all these matters and many other topics as well." The celebrated hemispheres experiment was, as noted in the biographical section above, carried out between July 1656 and August 1657. In Chapter IV of Book III he describes a new and much improved design of vacuum pump and attributes its invention to the need for a more easily transportable machine with which he could demonstrate his experiments to Frederick William, who had expressed the desire to see them. The new pump is also described on p. 67 of the Technica Curiosa. The demonstration in the Elector's Library at Cölln an der Spree took place in November 1663 and was recorded by a tutor to the Elector's sons. (Schneider p. 113.) A number of experiments, such as the rather cruel testing of the effect of a vacuum on birds and fish (Experimenta Nova, Book III, Chapter XVI), are not described in the Technica Curiosa. Although the Experimenta Nova does contain correspondence from 1665, there is no reason to doubt von Guericke's assertion that the work was essentially finished by March 1663.

Throughout Books II and III he returns again and again to the theme of there being no abhorrence of a vacuum and that all the phenomena explained by this supposed principle are in fact attributable to the pressure of the atmosphere in conjunction with various incorporeal potencies which he held to be acting. Thus the Earth's "conservative potency" (virtus conservativa) provided the explanation for the fact that the Earth retains its atmosphere though travelling through space. In countering the objection of a Dr. Deusing that the weight of the atmosphere would simply crush the bodies of all living things, he shows explicit awareness of the key property of a fluid – that it exerts pressure equally across all planes. In Chapter XXX of Book III he writes: "Dr. Deusing ought to have borne in mind that the air does not just press on our heads but flows all around us. Just as it presses from above on the head, it likewise presses on the soles of the feet from below and simultaneously on all parts of the body from all directions."

In the Experimenta Nova, Book III, Chapter 20, von Guericke reports on a barometer he had constructed and its application to weather forecasting. The earliest reference to his barometer is in a letter to Fr. Schott of November 1661 (Technica Curiosa, p. 37) where he writes: "I have observed the variation in the weight of the air by using a little man (i.e. a statue in the form of one) who hangs from a wall in my hypocaust where it floats on air in a glass tube and uses a finger to show the weight or lightness of the air. At the same time it indicates whether or not it is raining in nearby localities or whether there is unusually stormy weather at sea." In a subsequent letter of December 30, 1661 (Technica Curiosa p. 52) he gives a somewhat amplified account. His barometer thus prepared the way for meteorology. His later works focused on electricity. He invented the "Elektrisiermaschine", a version of which is illustrated in the engraving by Hubert-François Gravelot, c. 1750. This device, which is usually identified as the first electrostatic generator, was developed as part of von Guericke's interest in the worldly powers (mundane virtues) that operated in the universe.[14] Von Guericke also showed that electrical (magnetic) attraction does not require a medium to operate in[3] by an experiment using electrical transmission through linen thread.[8]^{:218, fn. 29}

Guericke's experiments with the sulfur globe published 1672

Von Guericke thought of the capacity of body to exert an influence beyond its immediate boundaries in terms of "corporeal and incorporeal potencies". Examples of "corporeal potencies" were the giving off of fumes, smells, gases etc. by bodies. An example of an "incorporeal potencies" was the Earth's "conservative potency" whereby it retained its atmosphere and caused the return of objects thrown upwards to the Earth's surface. The Earth also possessed an "expulsive potency" which was deemed to explain why objects that fall bounce back up again. The notion of an "incorporeal potency" is similar to that of "action at a distance", except the former notion remained purely qualitative and there is no inkling of the fundamental "action and reaction" principle.

Von Guericke describes his work on electrostatics in Chapter 15 of Book IV of the Experimenta Nova. In a letter of November 1661 to Fr. Schott, reproduced in the Technica Curiosa, he notes that the then projected Book IV would be concerned with "cosmic potencies" (virtutes mundanae). Accepting the claim of the preface to the Experimenta Nova that the entire work had been essentially completed before March 1663, von Guericke can be fairly credited with inventing a primitive form of frictional electrical machine before 1663. His electrostatic generator was created using a sulphur globe attached to an iron rod. By rubbing the sphere with a dry hand, von Guericke was able to impart a charge imbalance on the surface, which would allow him to attract and repel other objects.[15]

In Chapter 6 of Book IV von Guericke writes: "It seems reasonable to suppose that if the Earth has a fitting and appropriate attractive potency it will also have a potency of repelling things that might be dangerous or disagreeable to it. This is to be seen in the case of the sulphur sphere described below in Chapter 15. When that sphere is stroked or rubbed not only does it attract all light objects, but it sometimes arbitrarily also repels them before attracting them again. Sometimes indeed it doesn't even attract them again." Von Guericke was aware of both Gilbert's book On the Magnet and Magnetic bodies and on the great magnet the Earth published in 1600 and of the Jesuit Niccolo Cabeo's Philosophia Magnetica (1629). He does not explicitly acknowledge any anticipation of his demonstration of electrostatic repulsion by the latter but, as he quotes a passage from the same page, could not have been unaware that, in a discussion of the nature of electrical attraction, Cabeo had written (Philosophia Magnetica, p. 192): "When we see that small bodies (corpuscula) are lifted (sublevari et attolli) above the amber and also fall back to the motionless amber, it cannot be said that such erratic behaviour (talem matum – but if "matum" is taken as a misprint for "motum", then the translation is simply "such motion") is an attraction by the gravity of the attracting body." In Book IV, Chapter 8 of the Experimenta Nova von Guericke is at pains to point out the difference between his own "incorporeal potency" views and Cabeo's more Aristotelian conclusions. He writes: "Writers who have written on magnetism, always confuse it with electrical attraction, although there is a great difference. In particular, Gilbert in his book De Magnete claims that electrical attraction is caused by the effluence of a humour, that the humid seeks the humid and this is the cause of the attraction. Moreover in Philosophia Magnetica, Book 2, Chapter 21, Cabeo criticises Gilbert but does admit that this attraction is created by the agency of an effluent. Humidity does not play any role but the attraction is brought about purely by the agency of an effluent, by which the air is disturbed. After the initial impulse, the air returns to the amber again taking with it little particles. He (Cabeo) concludes by saying: 'I say therefore that from amber or any other electrically attracting body, a very rarefied effluent is emitted which dispels and attenuates the air, extremely agitating it. Then the agitated and attenuated air returns to the amber body sweeping along with it whatever dust or small bodies are in its way'. We however, who in the previous chapter, take the attraction of the sulphur ball as electrical in nature and operating through a conservative potency, cannot admit that the air plays a role in producing the attraction. Experiment visibly shows that this sulphur globe (once it has been rubbed) also exercises its potency through a linen cord up to a range of a cubit and more and can attract at that distance." Unknown to them at the time, this "mysterious" attraction and repulsion they had been witnessing was actually electrical conduction.[5]

The key Chapter 15 is entitled "On an experiment, in which these potencies, listed above, can be evoked by the rubbing of a sulphur ball." In Section 3 of this chapter he describes how light bodies are repelled from a sulphur sphere which has been rubbed with a dry hand, and are not again attracted until they have touched another body. Oldenburg's review of the Experimenta Nova (November 1672) in the Proceedings of the Royal Society sceptically observes: "How far this globe may be confided in, the Tryals and Consideration of some ingenious person here may perhaps inform us hereafter." In fact, Robert Boyle repeated von Guericke's experiments for the Royal Society in November 1672 and February 1673 (Schneider p. 127).