Demystyfing Air: First step to the Atomic Theory
Seventeenth century is important in World’s history for three important reasons. It was the century when Baroque form of art flourished. It was also the century when the Dutch people attained world supremacy, and above all, it was the age of scientific revolution; when with rapid developments in mathematics, physics, chemistry, astronomy, biology, modern science emerged and changed the World’s view of nature and society.
Baroque form of art was initiated by the Catholic Church as a counter reformation movement to the Protestant reformation movement. In 1517, Martin Luther,[1] professor of theology at the University of Wittenberg, published the famous “Ninety-five Thesis.” In the thesis he severely criticised several corrupt practices of the then Catholic Churches, in particular, the catholic way of dispensation of “indulgences[2].” That publication started the Protestant reformation movement which challenged the Papal authority, questioned the Catholic Church’s ability to define Christian practices. Even though started in Germany, the protestant reformation movement quickly spread throughout the central Europe. Catholic Church, to reassert themselves, launched a counter-reformation movement. Pope Paul III (reigned 1534-1549), considered to be the first pope of the counter-reformation, tried to address the issues raised by the Lutherians in an effective way. In 1545 he convened a convention of Clergymen. It was held in the Italian city of Trent and is known as Council of Trent. Between 1546 and 1563, the council met for 25 times and played an important part in defining Roman Catholic faith. Pope Paul III ask the council to define doctrine, correct morals, restore peace among Christians, and repel infidels. The council introduced various measures to regulate the Catholic Churches, e.g. training for the priests, disciplinary measures against luxurious living of church authorities, prescriptions for pastoral care and administration of churches. However, the measures could not quell the Lutherians dissidence and in 1918, the most destructive religious war started between the then fragmented European states. The war is known as thirt year’s was as it continued for thitry long years war ending in 1648. From then on, European states were left free to choose Catholism or Lutheranism as their state religion.
Early in the counter-reformaton movement the Catholic Church realised that “art” can help to restore the people’s faith. In Trent council, it was decided that ‘art’ should communicate directly and indirectly, the religious ideas and opinions of the Catholic Church, and the result was the Baroque art movement. The term Baroque was derived from the Portuguese `barocco’ meaning `irregular pearl or stone.’ In informal usage, baroque means elaborate or complex. To fulfil the catholic propaganda, and to impress the general populace, Baroque art form was styled in grandeur; rich in color, with great contrast; intense in light and shadows, projecting triumph, power and control and glorified both church and monarchy.
Seventeenth century was also the time of Dutch Golden age. Untill 17th century Dutch people were under the rule of Spanish Monarchy. Spanish monarchs used to rule from the house of Habsburg, one of the most influential royal houses of middle age Europe and the Spanish history over the 16th and 17th centuries (1516-1700) is usually called Habsburg Spain. Spain was predominantly Catholic while the Dutch people were Protestant. In his zeal to introduce Catholic way of life, King Phillip II introduced several harsh measures including Spanish Inqusition. The measures were resented by the Dutch people and in 1568, they revolted against the Spanish rule. With the exception of twelve years truce (1609-1621), the Dutch war of independence war continued for 80 long years (hence it is also known as Eighty years’ war). Finally, in 1648 Dutch people gained independence. For the Dutch, the first half of the 17th century was spent fighting the Spanish army, and in the second half in building the nation. Such was the zeal of their people that within a short time, the Dutch nation became of the wealthiest and most powerful nation in the world. They became World leader in navigation, science, arts. There are several reasons for the Dutch Golden Age and primarily among them was the migration of skilled labours and traders (who were predominantly protestant) to Holland to evade Catholic persecution. The protestant culture of thrift and education also helped the nation.
Seventeenth century was also the age of scientific revolution. Emergence of modern science with rapid developments in mathematics, physics, chemistry, astronomy, biology changed the World’s view of nature and society. Though debated, the 1543 publication of Nicolaus Copernicus’[3] De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) is often considered as the beginning of the scientific revolution. The revolution continued through Galileo Galilei’s[4] “Dialogue concerning the two chief World’s systems” published in 1632, and terminated in 17th century with publication of Isaac Newton’s[5] “Principia” in 1687. In the 17th century mankind also obtained the first experimental evidence for the atomic structure of matter, long back proposed by Greek philosopher Democritus (ca.460-370 BC) and put the theory on a firm footing. That evidence came from Torricelli’s discovery that air could support a column of mercury of about 30 inches high. The discovery nullified the long held Aristotelian belief that nature abhors vacumm or horror vacui. It also conclusively proved that air has weight, until then a controversial result.
Figure 1. Evangelista Torricelli. Picture from Wikipedia.
Evangelista Torricelli (15 October 1608-25 October 1647), was born in Rome in an impoverished family. He was the eldest of three sons of his father Gaspare Ruberti, a textile worker and mother Giacoma (Jacoba) Torricelli. It was fortunate that his father recognized the extraordinary ability of his eldest son and entrusted his education to his brother Jacapo. Jacapo was a monk in the Benedictine Church (Churches which follow rules of St. Benedict) at Faenza, an Italian city. Under the watchful eyes of the Jesuits, Torricelli had a sound education in mathematics and philosophy. He was a talented student and recognising his extra-ordinary ability, Benedictine Benedetto Castelli of the University of Sapienza in Rome[6] took him as secretary; a post young Torricelli held between 1626 to 1632. Benedetto Castelli was a student of Galileo and used to have regular communication with him. In 1632, while Castelli was away from Rome, Torricelli received a letter from Galileo. As secretary of Castelli, Torricelli wrote back to Galileo informing him of Castelli’s absence and took the opportunity to introduce himself. He wrote that he was a professional mathematician and studied the all the classical as well as contemporary texts, including Galileo’s recently published book; Dialogue Concerning the Two Chief Systems of the World – Ptolemaic and Copernican. He also expressed his belief on the Copernican theory. However, Torricelli was an ambitious man, and when in 1633 the Catholic Church indicted Galileo of heresy for supporting the Copernican theory, he realised that it would be dangerous to continue his interests in the Copernican theory. He deliberately shifted his attention to less controversial mathematical areas.
From 1632-1641, Torricelli served as secretary to Giovanni Ciampoli[7]. Ciampoli was exiled from Rome and was forced to travel to various places. Torricelli, as his secretary also travelled with him. During this period, he investigated in details the theory of motion, and completed the treatise, ‘De Motu Gravium,’ which later was included in his three part treatise “Opera Geometrica.” In 1641 Torricelli returned to Rome. In the mean time, Castelli forwarded a copy of Torricelli’s “De Motu” to Galileo as recommended his for a position under Galileo. Galileo was impressed by Torricelli’s “De Motu” and offered him secretaryship. However, death of Torricelli’s mother delayed his departure and only on 10 October 1641 Torricelli arrived at Florence. He served as Galileo’s secretary until his death in January 1642. On Galileo’s death Torricelli succeeded him as the court mathematician to Grand Duke Ferdinando II of Tuscany. He held this post until his death on 25th October 1647.
Torricelli is most remembered for inventing “mercury barometer,” an instrument to measure atmospheric pressure. The invention was the outcome of his investigation into an old problem; “Why a suction pump cannot lift water to a height greater than 32 foot?” The problem was given to Galileo and he gave a wrong answer. Galileo believed in Aristotle’s dictum of horror vacui (“nature abhors a vacuum”). He thought that power of vacuum held the water up. In analogy that a chord could support only so much weight and breaks if the weight exceeds a critical value, Galileo proposed that power of vacuum can held only a certain height of water. Increase the height, the amount of water simply became too much and the power of vacuum could not hold any more. Torricelli however did not agree with Aristotle’s dictum of “horror vacui”. In a letter to his friend Michelangelo Ricci[8] he wrote,
“Many have argued that a vacuum does not exist, others claim it exists only with difficulty in spite of the repugnance of nature; I know of no one who claims it easily exists without any resistance from nature.”
Torricelli was also interested to make an instrument which will exhibit changes in the atmosphere, which is sometimes heavier and denser and at other times lighter and thinner.
After studying all the previous experiments, Torricelli designed his own. He decided to do his experiments with mercury. He knew that experiments with water will require contraptions over 32 foot high which may make his neighbours suspicious of his activities and he may be accused of witchcraft. Indeed, 16th century Europe was highly superstitious. In 200 years beginning from mid 15th century more than 40000 Europeans (mostly female and few men) suffered cruel death on being accused of witchcraft.
Figure 2. Torricelli’s experimental arrangement.
Torricelli replaced water with mercury. Mercury is 13.6 times heavier and Torricelli correctly deduced that with mercury, his contraptions will be of much reduced height. Schematic diagram of his experiment is shown in Figure 2 . He filled a glass tube 4 feet (1.2 m) long with mercury and inverted the tube into a dish full of mercury. He saw that mercury fell until column height was approximately 30 inch (76 cm). He correctly guessed that the mercury column can rise only upto 30 inch due to external or atmospheric pressure of air. What about the empty space above the column of mercury? Torricelli argued that the space above the mercury must be vacuum and nothing else. Now, if vacuum is responsible for holding up the mercury column then with different shapes of the end tube, height of mercury will differ. He used two tubes, one with a simple blind end and the other with a small sphere on the end as shown in Figure 2, but the height of the mercury column remained same. Torricelli went on to argue that the vacuum was irrelevant to maintaining the height of the mercury column. He wrote to his friend Ricci,
“I claim that the force which keeps the mercury from falling is external and that the force comes from outside the tube. On the surface of the mercury which is in the bowl rests the weight of a column of fifty miles of air. Is it a surprise that into the vessel, in which the mercury has no inclination and no repugnance, not even the slightest, to being there, it should enter and should rise in a column high enough to make equilibrium with the weight of the external air which forces it up?
Torricelli also noticed that the height of mercury column changes with time. He correctly reasoned that the change is associated with the change in atmospheric pressure. This observation led to the discovery of “Barometer,” an instrument that measures air pressure. The name was coined and popularised by the British chemist Robert Boyle by fusing two Greek words: ‘baros’ meaning weight and ‘metron’ meaning measure. In today’s world, it is difficult to understand the implication Torricelli’s discovery. Any discovery can have two distinct implications: (i) add to the scientific body of knowledge, and (ii) change the prevailing opinions which are fundamental to the concept of nature. Discovery of the barometer did both. Undoubtedly, it added knowledge to the body of science. The discovery was hailed by sailors, as it gave them an instrument to predict weather and avoid disasters, saving precious men and cargo. It also changed the prevailing opinions on (i) vacuum or void; nature abhors vacuum, and (ii) air: air is weightless. Study of motion led Greeks to conceive the idea of void or vacuum. If a body was to move, there must be unoccupied space into which it could move, or conversely, when it move the space which it left must become empty. Aristotle argued that if the void is truly nothing it cannot exist: it is not possible to think that bodies are separated by what is itself nothing. There is thereof no void, space everywhere is full, a plenum. Thus he arrived at his dictum; “horror vacui” or “nature abhors void”. There is another reason, a religious one. Unfilled space or void was thought to be incompatible with the idea of “omnipotent” God. Giordano Bruno asked, “Why should or how can we suppose the divine potency to be idle?” Gottfried Leibniz, the French mathematician and philosopher, by a direct appeal to the law of continuity declared, “Within this world no gaps of any sort could be admitted.” Concept of empty space where God might have put matter but did not could not be accepted. For atomist, however, existence of void or vacuum was necessary. Unless there is void or vacuum, how and where would the atoms move; motion of atoms will be impossible. Torricelli, by creating a sustainable vacuum dispelled the long held misconception of “horror vacui” and for the first time created a foothold for the atomists.
Discovery of barometer also settled the controversy about the weight of air. Aristotle attributed a natural place to the terrestrial elements:, earth: centre of the Universe, water: above the earth in concentric cells, air: in concentric cells, above the water above the earth and fire: still above the air. Natural places are not merely places for Aristotle; they have influences or potency. This potency cause the elements to tend to return to their natural places, unless hindered. Thus, motion of bodies is either violent when imparted by other or natural; when it tend to return to its natural place. Air was naturally ‘light’ as its natural place is above earth and water. Air also tends to rise and relatively it seems to have no weight. It was then largely believed air is weightless. However, Aristotle believed contrarily. In “Physics” he wrote,
“In its own place each of these bodies has weight except fire, even air. Of this we have evidence in the fact that a bladder when inflated weighs more than when empty.”
However, Aristotle may have believed the right for the wrong reasons. Galileo was sceptical about Aristototle’s bladder experiment. He said,
“I am inclined to believe that the increase of weight observed in the leather bottle or bladder arises, not from the gravity of the air, but from the many thick vapors mingled with it in these lower regions. To this I would attribute the increase in weight in the leather bottle.”
Indeed, Aristotle’s bladder experiment was misleading. The inflated bladder contained compressed air; not air at normal pressure. Torricelli’s experiment proved beyond doubt that air has weight. He had the wisdom to declare:
“We live submerged at the bottom of an ocean of the element air, which by unquestioned experiments is known to have weight.”
[1] Martin Luther (10 Nov. 1483-18 Feb.1546) was a German professor of theology and a seminal figure in the Protestant reformation movement. His father, a miner and ore smelter, wanted his son to be a lawyer and provided him the best education he could. Martin obtained a MA degree from University of Erfurt and was on the way to became a lawyer, but a spiritual experience altered his course of life and he became a monk. According to his own admission, on July 2nd, 1505, while returning home from University, he was caught-up in a severe, life threatening storm. Fearing his life, he cried out to St, Anna, the patron saint of miners; “Help, Saint Anna, I will become a monk.” The storm subsided and Luther, much to the disappointment of his father, decided to keep his promise and became a monk. However, Luther didn’t find the religious enlightment he was seeking. He was disillusioned and discouraged by the immorality and corruption among the Catholic priests. He took a leave from monastery and joined University of Wittenberg for further studies. In 1512 he obtained a PhD and became a Professor of Theology at the University. He continued his spiritual investigations and finally realized that the key to spiritual salvation was not to fear God or be enslaved by religious dogma but to believe that faith alone would bring salvation. In 1517 he published, now the famous 95 thesis which started the protestant reformation movement. As the protestant movement gained momentum, pope officially excommunicated and declared him a heretic. He became a wanted man. But undeterred, in 1522, with the help of his friend and followers Luther organized the Lutherian Church and over the year, Lutherian church grew.
[2] In the teaching of the Roman Catholic Church, indulgence is “a way to reduce the amount of punishment one has to undergo for sins”. It may reduce the temporal punishment after death, in the state or process of purification called Purgatory. By the late Middle Ages, the abuse of indulgences, mainly through commercialization, had become a serious problem which the Church recognized but was unable to restrain effectively.
[3] Nicolaus Copernicus (1473-1543) was a Polish astronomer who first proposed sun-centric model of Universe. For more information about Copernicus and his model of Universe see the book, “Cooking Cosmos; unravelling mysteries of the Universe,” World Scientific.
[4] Galileo Galilei (1564-16420) was an Italian polymath: mathematician, astronomer, physicist, and engineer. He is widely regarded as the father of modern science. For more information about Galileo and his contributions, see the book, “Cooking Cosmos; unravelling mysteries of the Universe,” World Scientific.
[5]English physicist, mathematician and philosopher Sir Isaac Newton (1642-1727) was one of the greatest scientist of modern era. More details about Newton can be found in the book, “Cooking Cosmos; unravelling mysteries of the Universe,” World Scientific.
[6] University of Sapienza of is one of the oldest University. Founded in 1303, by enrolment, it is also the largest University in Europe.
[7] Giovanni Caimpoli (1589-1643) was a priest, a poet and a humanist. He was closely associated with Galileo. He was a student of Galileo at Padua and Pisa, and later became a close friend. Giovanni Caimpoli was instrumental in obtaining permission from Pope Paul Urban VIII for publishing Galileo’s Dialogue. He convinced the Pope that Galileo had faithfully followed Pope’s directions concerning how the book was to be written. Later, when Pope decided that Galileo had deceived him about the book’s arguments, Ciampoli fell into disrepute. The Pope removed Ciampoli from his officeand exiled him from Rome.
[8] Michelangelo Ricci (1619-1682) was an Italian Mathematician and a Cardinal of the Roman Catholic Church. He was also educated under Castelli and became a lifelong friend of Torricelli. He used to keep close contact with contemporary scientists and mathematicians and played an important role is propagating Torricelli’s experiment and his ideas.
Cooking Cosmos 