Copyright © 1997, 1998 by John L. Park

{ Page references are to S. Sambursky (1956) "The Physical World of the Greeks" Princeton University Press. ISBN 0-691-02411-1.}

Around 440 BC, Leucippus of Miletus originated the atom concept. He and his pupil, Democritus (c460-371 BC) of Abdera, refined and extended it in future years. There are five major points to their atomic idea. Almost all of the original writings of Leucippus and Democritus are lost. About the only sources we have for their atomistic ideas are found in quotations of other writers.  [Leucippus status is questioned by some; Democritus is firmly established primarily through the writings of Aristotle, and Diogenes Laertius—jk.]

At this time Greek philosophy was about 150 years old, having emerged early in the sixth century BC, centered in the city of Miletus on the Ionian coast in Asia Minor (now Turkey). The earliest known Greek philosopher was Thales of Miletus.

The work of Leucippus and Democritus was further developed by Epicurus (341-270 BC) of Samos, who made the ideas more generally known. Aristotle (384-322 BC) quotes both of them extensively in arguing against their ideas. Much of what we know about their ideas comes to us in a poem titled "De Rerum Natura" (On the Nature of Things) written by Lucretius (c95-55 BC). This poem, lost for over 1000 years, was rediscovered in 1417.

You may find the Leonard translation of "De Rerum Natura" on-line, but it is a big file.

Point #1 - All matter is composed of atoms, which are bits of matter too small to be seen. These atoms CANNOT be further split into smaller portions.

Democritus quotes Leucippus: "The atomists hold that splitting stops when it reaches indivisible particles and does not go on infinitely." (p. 107)

In other words, there is a lower limit to the division of matter beyond which we cannot go. Atoms were impenetrably hard, meaning they could not be divided. In Greek, the prefix "a" means "not" and the word "tomos" means cut. Our word atom therefore comes from atomos, a Greek word meaning uncuttable.

Democritus reasoned that if matter could be infinitely divided, it was also subject to complete disintegration from which it can never be put back together. However, matter can be reintegrated.

Even though matter can be destroyed by repeated splitting, new things can be made by joining simpler pieces of matter together. The process of disintegration & reintegration is reversible.

The idea of reversibility means that there must be a lower limit to the splitting of matter. If matter can be split infinitely, there is nothing to stop it from going on forever and destroying all matter.

Only with a definite and finite lower limit to splitting do we keep a permament foundation of ultimate particles with which to build up everything we see. As Epicurus says:

"Therefore, we must not only do away with division into smaller and smaller parts to infinity, in order that we may not make all things weak, and so in the composition of aggregate bodies be compelled to crush and squander the things that exist into the non-existent...." (p. 108)

Epicurus also insisted on an upper limit for atoms - they are always invisible. Although no reason is given, it seems obvious enough: all matter that can be seen by humans is still divisible, therefore cannot be atoms.

Point #2 - There is a void, which is empty space between atoms.

Aristotle quotes Leucippus: "Unless there is a void with a separate being of its own, 'what is' cannot be moved-nor again can it be 'many', since there is nothing to keep things apart." (p. 108)

In other words, there is empty space between atoms. In modern times, we would use the word vacuum, although the Greeks did not.

Given that all matter is composed of atoms (the ultimate and unchanging particles), then all changes must be as a result of the movement of atoms. However, in order to move there must be a void-a space entirely empty of matter-through which atoms can move from place to place.

Point #3 - Atoms are completely solid.

It then follows that there can be no void inside an atom itself. Otherwise an atom would be subject to changes from outside and could disintegrate. Then, it would not be an atom.

We know this is incorrect. In 1911, Ernest Rutherford discovered the nucleus, demonstrating in the process that a single atom is mostly empty space.

Point #4 - Atoms are homogeneous, with no internal structure.

The absolute solidity of the atoms also leads to the notion that atoms are homogeneous, or the same all the way through. Another way to express this is that an atom would have no internal structure.

Although there was speculation about sub-atomic structure in the 1800's after John Dalton introduced the atom idea on a solid scientific basis, it was not until 1897 and J.J. Thomson's discovery of the electron that the atom was shown to have an internal structure.

Point #5 - Atoms are different in ...

1) ...their sizes. See the Democritus quote just below.

2) ...their shapes. According to Aristotle: "Democritus and Leucippus say that there are indivisible bodies, infinite both in number and in the varieties of their shapes...." (p. 110)

Democritus says of atoms: "They have all sorts of shapes and appearences and different sizes.... Some are rough, some hook-shaped, some concave, some convex and some have other innumerable variations." (p. 110-111)

3) ...their weight. Again from Aristotle: "Democritus recognized only two basic properties of the atom: size and shape. But Epicurus added weight as a third. For, according to him, the bodies move by necessity through the force of weight." (p. 111)

Concluding Remarks

The idea of the atom was strongly opposed by Aristotle and others. Because of this, the atom receeded into the background. Although there is a fairly continuous pattern of atomistic thought through the ages, only a relative few scholars gave it much thought.

Due to complex circumstances beyond the scope of this lesson, the Catholic Church accepted Aristotle's position and came to equate atomistic ideas with Godlessness. For example, "Democritus of Abdera said that there is no end to the universe, since it was not created by any outside power."

It was not until 1660 that Pierre Gassendi succeeded in separating the two and not until 1803 that John Dalton put the atom on a solid scientific basis.

I. Atomism in Antiquity

The atomic ideas of Leucippus and Democritus (from about 440 BC) were opposed by Aristotle about 100 years or so later. Those who acknowledged Aristotle as their master opposed atoms. Since Epicurus was an atomist, he was opposed by his rivals, the Stoics. Cicero, Seneca and Galen all spoke against atoms.

Hero of Alexandria (150 A.D.?) makes use of atoms to explain compression and rarefaction (to thin something out; become less dense). Hero denied the existence of an extended vacuum, but allowed for a vacuum between atoms. One proof he cited was that fire could enter into a material, showing that it had openings, i.e., a vacuum. He pointed out that the pores of a diamond were too small to let in fire and so the stone was incombustible. (In the 1700's, both Lavosier and Priestly were able to burn diamonds with large lenses that concentrated the sunlight.)

Important figures within the Church spoke against atoms. Dionysios (Bishop of Alexandria 200 A.D.), Lactantius (died 324 A.D.) and Augustine (354-430 A.D.) are names cited by Partington.

II. Atomism in the Middle Ages

Isidore, Bishop of Seville (560-636), the Venerable Bede (672-735), and Hrabanus Maurus (776-856) all used the word "atom" to refer to discontunities in bodies. William of Conches (1080-1154) and Vincent of Beauvais (died ca. 1264-8) both showed knowledge of atomic thinking in their writing. William openly taught about the ideas of Democritus. Vincent wrote a great encyclopedia, but only gave short quotations about atoms.

The works of Aristotle were rediscovered by Western Europe about 1200, in Latin translations of Arabic translations from the Greek. Much scholastic discussion followed among such people as St. Thomas Aquinas (1225-74) and Roger Bacon (1214-92). Over time, the Catholic Church began to elevate Aristotle's writings to the same level as Scripture and had associated atomic thinking with Godlessness. (Quite frankly, the ChemTeam does not know how the process took place, but it did. On a side issue, the Church also did the same thing with Ptolemy in astronomy. When Galileo opposed the Church (in the 1630's?), he was found guilty of heresy. Only recently (around the late 1980's-early 1990's) has the Church formally admitted its error.)

De Rerum Natura was rediscovered in 1417 (and printed in 1473, reprinted in 1486) and became the prime source (still true today) for the ideas of Leucippus and Democritus. You may ask how William of Conches knew of Democritus. Scattered about the libraries of churches in Europe were a few copies of De Rerum Natura. Stones, in his article, cites three known to have existed in William's lifetime. Other copies certainly also existed at that time.

III. Atomism in the Renaissance

A) Nicholas of Cusa (1401-1464) wrote:

"What dost thou understand by an atom?
"Under mental consideration that which is continuous becomes divided into the ever divisible, and the multitude of parts progresses to infinity. But by actual division we arrive at an actually indivisible part which I call an atom. For an atom is a quantity, which on account of its smallness is actually indivisible."

B) Girolamo Fracastoro (1478-1553) was a physician who wrote about atomism. In fact, the phrase "seeds of disease" is asociated with his name. In discussion the mechanism of infection, he supposed the existence of minute indivisible substances which convey the disease. he called these semina. Interestingly, Lucretius (in Book VI) refers to seeds helpful to life and seeds which cause disease and death. In a different book, Fracastoro indicates his agreement with Democritus and puts forward an atomistic point of view concerning chemical reactions.

C) Peter Ramus (1515-1572) broke with Aristotle early in his life. (Remember, the Catholic Church had long ago elevated Aristotle's works to Scripture. In essence, both were considered to be infallible.) At age 21, he presented a thesis based on this idea: "all that Aristotle has said is false." His opponents could not just appeal to the authority of Aristotle to refute him, since that would be begging the question. After attacking his ideas for a whole day and being refuted, Ramus was finally awarded his degree with honors.

In 1543, he wrote two books (aganist Aristotle) that provoked violent reaction. Their publication was banned, the books were burned, and Ramus was silenced by order of the Pope, Francis I. After the Pope died a year later, Ramus resumed teaching and was appointed professor in 1551.

However, he embraced the Reformed faith (Martin Luther had nailed his "95 Theses" to church door at the University of Wittenberg on October 31, 1517.) and was forced to flee from Paris. His home was pillaged and his library burned. He returned eventually, but ultimately died in the massacre of St. Bartholomew in Paris in 1572.

Although it appears that Ramus did not write about atomism as such, he was in the forefront of the attack on the authority of Aristotle.

D) In 1588, Giordano Bruno wrote:

"The division of natural things has a limit; an indivisible something exists. The division of natural things attains the smallest and last parts which are not perceptible by the aid of human instruments."

E) Partington lists five other names of people alive through in the 1500's and 1600's who wrote about atoms. Of interest is Sebastin Basso, who wrote of particles of the first, second, and third order, that is to say, structures BUILT UP by bringing atoms together. What we might call a molecule today. J.C. Magnenus attempted to calculate the size of an atom.

F) Daniel Sennert (1572-1637) was an atomist during the time Rene Descartes (1596-1650) and Francis Bacon (1561-1626) were alive. Both Bacon and Descartes, although intellectual giants of that era, were not too convinced about atomism.

Sennert taught that there must be atoms of more than one type and that atoms joined together to form composite bodies (I think he called these secondary atoms, but I am not sure). He used the fact that vapor from wine penetrated 4 layers of paper to show the smallness of atoms. Another example was that a large volume of vapor yielded a small drop of liquid.

He also taught that atoms retain their essential form. For example, melt some pure gold and pure silver together until completely mixed. On treating the mixture with nitric acid, the silver is dissolved and the gold remains.

G) Partington dates the real beginning of the revival of atomic thinking to the invention of the barometer in 1634 by Evangalestia Torricelli. Above the mercury of the barometer was a vacuum. An important position of Aristotle (and the Church) was that the vacuum did not exist. This invention (and the air pump by Otto von Guericke in 1654) dealt a severe, if not crippling, blow to the non-existence of the vacuum.

IV. Pierre Gassendi (1592-1655)

Gassendi is considered by many to be the reviver of atomism, but as you have seen, atomism never really went away, it was just on the fringes. However, Gassendi was successful in making atomism more widely known and acceptable, especially by separating a belief in atomism from athesism.

Before going into his teachings, it is interesting to note that in 1624, the Parliment of Paris had issued a decree that anyone holding or teaching a position opposed to Aristotle (including atomism) was liable to be put to death. Gassendi has influential friends, so he was left alone.

In 1649 he published his major work on atomism: Syntagma philosophiae Epicuri. It is divided into three sections: Logic, Physics, and Ethics.

Before even discussing atoms, Gassendi devotes three chapters to discussing the void and its necessity. He dwells on Torricelli and his experiments at length.

He describes the Greek position: atoms cannot be created nor destroyed, they are solid, they have weight, and cannot be subdivided. Gassendi taught that atoms are not just geometric points, but that they have a definite size, although it is very small.

However, he differs from the Greeks in that atoms have not been in existence forever, but were made by God. The atoms move not a se ipsis (of themselves), but Dei gratia (as a gift of God). This is the idea which freed atomism from athesism.

Gassendi allows for the union of atoms to form groups, which he calls moleculae or corpuscula. However, these groups are not held together by attractive forces, but by mechanical forces such as hooks-and-eyes or antlers.

V. From Gassendi to Dalton: Just Under 150 years

Robert Boyle (1627-91) was an atomist, although he liked the word "corpuscle." In 1661, published the "Sceptical Chymist." In it, he insists that the chemical elements must be actual, physical substances rather than the "principles" the alchemists thought of (the "principle of salt", the "principle of gold" and so on). Boyle says:

"I can easily enough sublime gold into the form of red Chrystalls of a considerable length; and many other ways may Gold be disguis'd, and help to constitute Bodies of very different Natures both from It and from one another, and nevertheless be afterwards reduc'd to the self-same Numerical, Yellow, Fixt, Ponderous, and Malleable Gold as it was before its commixture."

Later on in the book, he says of atoms (oops, sorry Bob, corpuscles) of gold:

"though they may not be primary Concretions of the most minute Particles of matter, but confessedly mixt Bodies, are able to concurre plentifully in the composition of several very differing bodies without losing their own Nature or Texture, or having their cohesion violated by the divorce of their associated parts or ingredients.

Again, he says:

"the difference of Bodies may depend meerly upon that of the schemes whereinto their Common matter is put . . . so that according as the small parts of matter reccede from each other, or work upon each other . . . a Body of this or that denomination is producd."

Incidently, two of the last non-believers in the reality of atoms were Wilhelm Ostwald and Ernst Mach. (I am not including those who are not in the mainstream of science, Ostwald and Mach were both respected scientists.) In 1908, Ostwald explicitly stated his belief in the reality of atoms in the introduction to his textbook Outline of General Chemistry. In 1915, Mach was still writing in an anti-atomistic way. The following year, Mach died, aged 78.

Since then, no one of any scientific substance has questioned the reality of atoms.

In 1803, John Dalton of England introduced the atomic idea to chemistry (and is called the Father of Modern Atomic Theory for his efforts). However, it would be false to assume that atomic ideas disappeared completely from the intellectual map for over 2000 years. For, although atomic thinkers between the Greeks and Dalton were few, there is a fairly continuous line from the Greeks to John Dalton.

Copyright © 1997, 1998 by John L. Park

{ Page references are to S. Sambursky (1956) "The Physical World of the Greeks" Princeton University Press. ISBN 0-691-02411-1.}

Around 440 BC, Leucippus of Miletus originated the atom concept. He and his pupil, Democritus (c460-371 BC) of Abdera, refined and extended it in future years. There are five major points to their atomic idea. Almost all of the original writings of Leucippus and Democritus are lost. About the only sources we have for their atomistic ideas are found in quotations of other writers.  [Leucippus status is questioned by some; Democritus is firmly established primarily through the writings of Aristotle, and Diogenes Laertius—jk.]

At this time Greek philosophy was about 150 years old, having emerged early in the sixth century BC, centered in the city of Miletus on the Ionian coast in Asia Minor (now Turkey). The earliest known Greek philosopher was Thales of Miletus.

The work of Leucippus and Democritus was further developed by Epicurus (341-270 BC) of Samos, who made the ideas more generally known. Aristotle (384-322 BC) quotes both of them extensively in arguing against their ideas. Much of what we know about their ideas comes to us in a poem titled "De Rerum Natura" (On the Nature of Things) written by Lucretius (c95-55 BC). This poem, lost for over 1000 years, was rediscovered in 1417.

You may find the Leonard translation of "De Rerum Natura" on-line, but it is a big file.

Point #1 - All matter is composed of atoms, which are bits of matter too small to be seen. These atoms CANNOT be further split into smaller portions.

Democritus quotes Leucippus: "The atomists hold that splitting stops when it reaches indivisible particles and does not go on infinitely." (p. 107)  In other words, there is a lower limit to the division of matter beyond which we cannot go. Atoms were impenetrably hard, meaning they could not be divided. In Greek, the prefix "a" means "not" and the word "tomos" means cut. Our word atom therefore comes from atomos, a Greek word meaning uncuttable.  Democritus reasoned that if matter could be infinitely divided, it was also subject to complete disintegration from which it can never be put back together. However, matter can be reintegrated.  Even though matter can be destroyed by repeated splitting, new things can be made by joining simpler pieces of matter together. The process of disintegration & reintegration is reversible.The idea of reversibility means that there must be a lower limit to the splitting of matter. If matter can be split infinitely, there is nothing to stop it from going on forever and destroying all matter.Only with a definite and finite lower limit to splitting do we keep a permament foundation of ultimate particles with which to build up everything we see. As Epicurus says:  "Therefore, we must not only do away with division into smaller and smaller parts to infinity, in order that we may not make all things weak, and so in the composition of aggregate bodies be compelled to crush and squander the things that exist into the non-existent...." (p. 108)

Epicurus also insisted on an upper limit for atoms - they are always invisible. Although no reason is given, it seems obvious enough: all matter that can be seen by humans is still divisible, therefore cannot be atoms.

Point #2 - There is a void, which is empty space between atoms.

Aristotle quotes Leucippus: "Unless there is a void with a separate being of its own, 'what is' cannot be moved-nor again can it be 'many', since there is nothing to keep things apart." (p. 108)  In other words, there is empty space between atoms. In modern times, we would use the word vacuum, although the Greeks did not.  Given that all matter is composed of atoms (the ultimate and unchanging particles), then all changes must be as a result of the movement of atoms. However, in order to move there must be a void-a space entirely empty of matter-through which atoms can move from place to place.

Point #3 - Atoms are completely solid.

It then follows that there can be no void inside an atom itself. Otherwise an atom would be subject to changes from outside and could disintegrate. Then, it would not be an atom.

We know this is incorrect. In 1911, Ernest Rutherford discovered the nucleus, demonstrating in the process that a single atom is mostly empty space.

Point #4 - Atoms are homogeneous, with no internal structure.

The absolute solidity of the atoms also leads to the notion that atoms are homogeneous, or the same all the way through. Another way to express this is that an atom would have no internal structure.

Although there was speculation about sub-atomic structure in the 1800's after John Dalton introduced the atom idea on a solid scientific basis, it was not until 1897 and J.J. Thomson's discovery of the electron that the atom was shown to have an internal structure.

Point #5 - Atoms are different in ...

1) ...their sizes. See the Democritus quote just below.

2) ...their shapes. According to Aristotle: "Democritus and Leucippus say that there are indivisible bodies, infinite both in number and in the varieties of their shapes...." (p. 110)

Democritus says of atoms: "They have all sorts of shapes and appearences and different sizes.... Some are rough, some hook-shaped, some concave, some convex and some have other innumerable variations." (p. 110-111)

3) ...their weight. Again from Aristotle: "Democritus recognized only two basic properties of the atom: size and shape. But Epicurus added weight as a third. For, according to him, the bodies move by necessity through the force of weight." (p. 111)

Concluding Remarks

The idea of the atom was strongly opposed by Aristotle and others. Because of this, the atom receeded into the background. Although there is a fairly continuous pattern of atomistic thought through the ages, only a relative few scholars gave it much thought.

Due to complex circumstances beyond the scope of this lesson, the Catholic Church accepted Aristotle's position and came to equate atomistic ideas with Godlessness. For example, "Democritus of Abdera said that there is no end to the universe, since it was not created by any outside power."

It was not until 1660 that Pierre Gassendi succeeded in separating the two and not until 1803 that John Dalton put the atom on a solid scientific basis.

I. Atomism in Antiquity

The atomic ideas of Leucippus and Democritus (from about 440 BC) were opposed by Aristotle about 100 years or so later. Those who acknowledged Aristotle as their master opposed atoms. Since Epicurus was an atomist, he was opposed by his rivals, the Stoics. Cicero, Seneca and Galen all spoke against atoms.

Hero of Alexandria (150 A.D.?) makes use of atoms to explain compression and rarefaction (to thin something out; become less dense). Hero denied the existence of an extended vacuum, but allowed for a vacuum between atoms. One proof he cited was that fire could enter into a material, showing that it had openings, i.e., a vacuum. He pointed out that the pores of a diamond were too small to let in fire and so the stone was incombustible. (In the 1700's, both Lavosier and Priestly were able to burn diamonds with large lenses that concentrated the sunlight.)

Important figures within the Church spoke against atoms. Dionysios (Bishop of Alexandria 200 A.D.), Lactantius (died 324 A.D.) and Augustine (354-430 A.D.) are names cited by Partington.

II. Atomism in the Middle Ages

Isidore, Bishop of Seville (560-636), the Venerable Bede (672-735), and Hrabanus Maurus (776-856) all used the word "atom" to refer to discontunities in bodies. William of Conches (1080-1154) and Vincent of Beauvais (died ca. 1264-8) both showed knowledge of atomic thinking in their writing. William openly taught about the ideas of Democritus. Vincent wrote a great encyclopedia, but only gave short quotations about atoms.

The works of Aristotle were rediscovered by Western Europe about 1200, in Latin translations of Arabic translations from the Greek. Much scholastic discussion followed among such people as St. Thomas Aquinas (1225-74) and Roger Bacon (1214-92). Over time, the Catholic Church began to elevate Aristotle's writings to the same level as Scripture and had associated atomic thinking with Godlessness. (Quite frankly, the ChemTeam does not know how the process took place, but it did. On a side issue, the Church also did the same thing with Ptolemy in astronomy. When Galileo opposed the Church (in the 1630's?), he was found guilty of heresy. Only recently (around the late 1980's-early 1990's) has the Church formally admitted its error.)

De Rerum Natura was rediscovered in 1417 (and printed in 1473, reprinted in 1486) and became the prime source (still true today) for the ideas of Leucippus and Democritus. You may ask how William of Conches knew of Democritus. Scattered about the libraries of churches in Europe were a few copies of De Rerum Natura. Stones, in his article, cites three known to have existed in William's lifetime. Other copies certainly also existed at that time.

III. Atomism in the Renaissance

A) Nicholas of Cusa (1401-1464) wrote:

"What dost thou understand by an atom?
"Under mental consideration that which is continuous becomes divided into the ever divisible, and the multitude of parts progresses to infinity. But by actual division we arrive at an actually indivisible part which I call an atom. For an atom is a quantity, which on account of its smallness is actually indivisible."

B) Girolamo Fracastoro (1478-1553) was a physician who wrote about atomism. In fact, the phrase "seeds of disease" is asociated with his name. In discussion the mechanism of infection, he supposed the existence of minute indivisible substances which convey the disease. he called these semina. Interestingly, Lucretius (in Book VI) refers to seeds helpful to life and seeds which cause disease and death. In a different book, Fracastoro indicates his agreement with Democritus and puts forward an atomistic point of view concerning chemical reactions.

C) Peter Ramus (1515-1572) broke with Aristotle early in his life. (Remember, the Catholic Church had long ago elevated Aristotle's works to Scripture. In essence, both were considered to be infallible.) At age 21, he presented a thesis based on this idea: "all that Aristotle has said is false." His opponents could not just appeal to the authority of Aristotle to refute him, since that would be begging the question. After attacking his ideas for a whole day and being refuted, Ramus was finally awarded his degree with honors.

In 1543, he wrote two books (aganist Aristotle) that provoked violent reaction. Their publication was banned, the books were burned, and Ramus was silenced by order of the Pope, Francis I. After the Pope died a year later, Ramus resumed teaching and was appointed professor in 1551.

However, he embraced the Reformed faith (Martin Luther had nailed his "95 Theses" to church door at the University of Wittenberg on October 31, 1517.) and was forced to flee from Paris. His home was pillaged and his library burned. He returned eventually, but ultimately died in the massacre of St. Bartholomew in Paris in 1572.

Although it appears that Ramus did not write about atomism as such, he was in the forefront of the attack on the authority of Aristotle.

D) In 1588, Giordano Bruno wrote:

"The division of natural things has a limit; an indivisible something exists. The division of natural things attains the smallest and last parts which are not perceptible by the aid of human instruments."

E) Partington lists five other names of people alive through in the 1500's and 1600's who wrote about atoms. Of interest is Sebastin Basso, who wrote of particles of the first, second, and third order, that is to say, structures BUILT UP by bringing atoms together. What we might call a molecule today. J.C. Magnenus attempted to calculate the size of an atom.

F) Daniel Sennert (1572-1637) was an atomist during the time Rene Descartes (1596-1650) and Francis Bacon (1561-1626) were alive. Both Bacon and Descartes, although intellectual giants of that era, were not too convinced about atomism.

Sennert taught that there must be atoms of more than one type and that atoms joined together to form composite bodies (I think he called these secondary atoms, but I am not sure). He used the fact that vapor from wine penetrated 4 layers of paper to show the smallness of atoms. Another example was that a large volume of vapor yielded a small drop of liquid.

He also taught that atoms retain their essential form. For example, melt some pure gold and pure silver together until completely mixed. On treating the mixture with nitric acid, the silver is dissolved and the gold remains.

G) Partington dates the real beginning of the revival of atomic thinking to the invention of the barometer in 1634 by Evangalestia Torricelli. Above the mercury of the barometer was a vacuum. An important position of Aristotle (and the Church) was that the vacuum did not exist. This invention (and the air pump by Otto von Guericke in 1654) dealt a severe, if not crippling, blow to the non-existence of the vacuum.

IV. Pierre Gassendi (1592-1655)

Gassendi is considered by many to be the reviver of atomism, but as you have seen, atomism never really went away, it was just on the fringes. However, Gassendi was successful in making atomism more widely known and acceptable, especially by separating a belief in atomism from athesism.

Before going into his teachings, it is interesting to note that in 1624, the Parliment of Paris had issued a decree that anyone holding or teaching a position opposed to Aristotle (including atomism) was liable to be put to death. Gassendi has influential friends, so he was left alone.

In 1649 he published his major work on atomism: Syntagma philosophiae Epicuri. It is divided into three sections: Logic, Physics, and Ethics.

Before even discussing atoms, Gassendi devotes three chapters to discussing the void and its necessity. He dwells on Torricelli and his experiments at length.

He describes the Greek position: atoms cannot be created nor destroyed, they are solid, they have weight, and cannot be subdivided. Gassendi taught that atoms are not just geometric points, but that they have a definite size, although it is very small.

However, he differs from the Greeks in that atoms have not been in existence forever, but were made by God. The atoms move not a se ipsis (of themselves), but Dei gratia (as a gift of God). This is the idea which freed atomism from athesism.

Gassendi allows for the union of atoms to form groups, which he calls moleculae or corpuscula. However, these groups are not held together by attractive forces, but by mechanical forces such as hooks-and-eyes or antlers.

V. From Gassendi to Dalton: Just Under 150 years

Robert Boyle (1627-91) was an atomist, although he liked the word "corpuscle." In 1661, published the "Sceptical Chymist." In it, he insists that the chemical elements must be actual, physical substances rather than the "principles" the alchemists thought of (the "principle of salt", the "principle of gold" and so on). Boyle says:

"I can easily enough sublime gold into the form of red Chrystalls of a considerable length; and many other ways may Gold be disguis'd, and help to constitute Bodies of very different Natures both from It and from one another, and nevertheless be afterwards reduc'd to the self-same Numerical, Yellow, Fixt, Ponderous, and Malleable Gold as it was before its commixture."

Later on in the book, he says of atoms (oops, sorry Bob, corpuscles) of gold:

"though they may not be primary Concretions of the most minute Particles of matter, but confessedly mixt Bodies, are able to concurre plentifully in the composition of several very differing bodies without losing their own Nature or Texture, or having their cohesion violated by the divorce of their associated parts or ingredients.

Again, he says:

"the difference of Bodies may depend meerly upon that of the schemes whereinto their Common matter is put . . . so that according as the small parts of matter reccede from each other, or work upon each other . . . a Body of this or that denomination is producd."

Incidently, two of the last non-believers in the reality of atoms were Wilhelm Ostwald and Ernst Mach. (I am not including those who are not in the mainstream of science, Ostwald and Mach were both respected scientists.) In 1908, Ostwald explicitly stated his belief in the reality of atoms in the introduction to his textbook Outline of General Chemistry. In 1915, Mach was still writing in an anti-atomistic way. The following year, Mach died, aged 78.

Since then, no one of any scientific substance has questioned the reality of atoms.

In 1803, John Dalton of England introduced the atomic idea to chemistry (and is called the Father of Modern Atomic Theory for his efforts). However, it would be false to assume that atomic ideas disappeared completely from the intellectual map for over 2000 years. For, although atomic thinkers between the Greeks and Dalton were few, there is a fairly continuous line from the Greeks to John Dalton.