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During the course of the seventeenth century, an
increasing number of natural philosophers turned to
one or another versions of the atomic doctrine as an
explanatory framework for natural phenomena. By the
end of the century, an overwhelming majority of natu-
ral philosophers no longer held serious doubts about
the existence of atoms in nature. The reasons for this
turn of events are numerous and complex, and the
depths of the problem are only now being explored
by historians of the period.

Atomism appealed to many men of the seventeenth
century on several levels. First of all, they saw in
atomism a systematic mode of explanation, sanctified
by time, with which they could confront the alterna-
tives of Aristotelianism and Paracelsianism which many
found intellectually stultifying and, because of the
adherents of these other paths, often socially unaccept-
able. Secondly, the relationships posited by atomism—
the motions and impacts of material objects—were
close to their experience with gross bodies. Further-
more, the intrusion of machines into the daily and
economic lives of men of the seventeenth century
became increasingly evident. Scientists draw the anal-
ogies employed in natural explanation from experience;
these machines, which illustrated impact or utilized
the presence of a vacuum provided an impetus for the
employment of a “mechanical” explanation. After such
explanation was decided upon, atomism provided a
way of interpreting those other phenomena which were
patently nonmechanical on the visible level. In short,
atomism was considered by its adherents over-
optimistically as more practical and more “realistic”
than its alternatives.

Simon Patrick, a member of the Royal Society of
London, illustrated this point in his Brief Account of
the New Sect of Latitude Men (1662). Patrick related
the story of a farmer whose clock was in need of repair.
He consulted a “Perpatetick artificer” who explained
the material, formal, and efficient causes of clocks, the
presence of the formal cause and its privation before
it was made. He went on to demonstrate that the
nature of the clock-work was a principle of motion
by an “inward device of its own accord,” and lacking
that, the broken clock was now indeed no clock at
all. The farmer's son, a university man, who had read
Magirus (a favorite late sixteenth-century Aristotelian
author), happened along and explained the matter and
form of the clock; its primary and secondary qualities;
the occult quality in the dial; its “sympathy” with bell,
etc. However, the clock remained broken. After a
while, the landlord came by. He, an ingenious gentle
man, was impatient with all the scholastic jargon and
explained to the farmer the true mechanical principles
of the clock. He told the son that “he should take no
more notice of the substantial forms and qualities of
a clock, and told him that he rejected principles, and
therefore would not dispute with him” (p. 19).

“How far,” Patrick concluded, “the Clock-menders
discourse resembles the Scholastick Philosophy or the
Gentlemans [sic] the atomicall, let others judge.” But,
he continued, “how can we satisfy our selves with the
four Elements of Aristotle, or the three principles of
the Chymists,...? Truly to them that have once
tasted of the Mechanical Philosophy, formes and qual-
ities are like to give as little satisfaction, as the Clock-
mender did to the Intelligent Gentleman in the Story”
(pp. 19-22). It should be made clear, however, that
the reception and establishment of the atomic doctrine
was neither so simple or rapid as Patrick's story may
have implied. The road was a somewhat rocky one and
the following will attempt to outline some of the major
events of that reception.

Atomism in the Renaissance. During the Middle
Ages the works of the great atomist and poet-
philosopher, Lucretius, were largely known second-
hand. Interest in his works, however, took a sharp turn
upward in the fifteenth century owing primarily to the
Italian humanist, Poggio Bracciolini. An apostolic sec-
retary to the Pope, Poggio explored the monasteries
of Europe in search of forgotten Latin manuscripts.
In the years around 1415, he apparently found a copy
of the original first-century (B.C.) work De rerum natura
(On the Nature of Things), of Lucretius. Gradually,
during the fifteenth century, this great work of atomist
philosophy became known throughout western Europe.
One of the earliest philosophers to study critically the
resurrected Lucretius was the Platonist, Marsilio
Ficino. In 1473, at Brescia, an edition of De rerum
natura appeared, and was swiftly followed by at least
three more by 1500. For the first time in many centu-
ries, a complete treatise of atomist natural philosophy
became available to western scholars.

Another important source of atomist thought in the
Renaissance was the Lives of the Philosophers, a third-
century work of Diogenes Laërtius which was first
printed in 1533. Diogenes' Lives includes those of
Democritus and Leucippus, and the entire tenth book
is devoted to the great Hellenistic atomist, Epicurus.
Included in the tenth book are letters from Epicurus
to Herodotus and Pythocles, the former being one of
the clearest and most concise statements of atomist
natural philosophy. In sum, ample writings of the
ancients became available in the sixteenth century to
fill out and encourage the interest in atomism which
had been increasing since Poggio's discovery. The in-

terest took several forms. At first, it was primarily
literary; the works of Montaigne and Edmund Spenser,
for example, demonstrate the influence of Lucretius.
It was not as a natural philosopher that European
savants accepted Lucretius; for them, Lucretius was
a sublime poet. As a philosopher he fell short of meet-
ing the minimum Christian requirements.

It was not until the writings of Giordano Bruno that
the atomists' view of the physical world began to hold
meaning for Western philosophers. Indeed, in the work
of Bruno, atomism became the key to understanding
the universe and its Creator. For Bruno, atomism was
the metaphysical principle on the basis of which the
underlying unity of all nature could be demonstrated.
In the minimum spiritual atom or monad he saw the
germ of all existence. The atom in its metaphysical
role is the matrix for all reality and, moreover, is the
substance of the soul. Through the agency of the
monad, God becomes the source for all change in
nature, as well as the source of its existence. If the
atom served a metaphysico-theological purpose in the
writings of Bruno, it also was utilized as a mathematical
and physical standard. In his De triplici minimo et
mensura (1591), the minimum has three senses: in
physics, mathematics, and metaphysics. In short, the
monad was the keystone of Bruno's all-embracing uni-
versal scheme.

The atom played an entirely different role in the
writings of certain other natural philosophers of the
late sixteenth and early seventeenth century. These
men, perhaps more recognizable in modern parlance
as “scientists,” utilized the concept of the atom as an
explanatory tool, a tool made necessary by what was
to them the demise of Aristotelianism. Of these new
atomists three stand out: Galileo Galilei, Thomas
Hariot, and Isaac Beeckman.

Beeckman and Hariot are two fascinating and un-
fortunately neglected scientific figures. Isaac was for-
tunate enough to have received a good education, and
later became master of the Latin school at Dordrecht.
Like his predecessor, Leonardo da Vinci, and his con-
temporary, Hariot, Beeckman published nothing of
scientific value in his lifetime. It is only with the post-
humous publication (in the twentieth century) of his
Journal that many of his interesting and important
researches have come to light. One of his most success-
ful endeavors was to derive the law of falling bodies;
E. J. Dijksterhuis has also shown that Beeckman arrived
at some form of the inertial principle. But what in-
terests us here is that behind Beeckman's physics
was an atomistic view of nature that was essentially
mechanical.

According to Beeckman, a vacuum must exist in
nature; directly in opposition to Aristotle, Beeckman
looked to the existence of motion to prove it. In this
void, matter consists of atomic parts. The qualities of
bodies depend on the magnitude, arrangement, and
motion of these atoms. For example, cold and heat
consist of the motion (or in the case of cold, the lack
of motion) of the constituent atoms. Wetness and dry-
ness are merely results of the figure or shape of the
atomic particles. Dry bodies are composed of sharp-
ened atoms; wet bodies of rounded ones. In fact, the
four so-called elements of the Aristotelians may easily
be derived from the differing shapes of atoms. Out of
a first kind comes air, fire by a second, earth by a third,
and water by a fourth type. Light and sound, moreover,
can be seen to have “material” causes. For example,
according to Beeckman the reflection and refraction
of light are caused by the interaction of light and the
atoms of gross matter. Beeckman's atomism, unlike that
of Bruno, was a philosophy intended for a specific
physical purpose: it was to replace those worn forms
and qualities of the scholastics which were unimagina-
ble or unpicturable in any physical way. It was not
an original atomic philosophy, nor did Beeckman em-
ploy it in any novel manner. His atomism was an ad
hoc device, invented to explain certain physical phe-
nomena—Beeckman's primary interest.

Similarly, the atomism of Thomas Hariot served as
a useful, physical hypothesis, invented to render un-
derstandable mathematical ideas and chemical and
physical phenomena. Hariot was born and educated
at Oxford, graduating from St. Mary's Hall in 1579.
After receiving his degree, he entered the service of
Sir Walter Raleigh as mathematical tutor. Raleigh
arranged for Hariot to accompany Grenville's voyage
to Virginia in 1585; there Hariot collected a great deal
of data concerning Virginia and its inhabitants. He
returned to England in 1586 and began writing his
Briefe and True Report of the New Found Land of
Virginia; it appeared in 1588, the only published work
of Hariot to appear in his lifetime.

Soon after returning to England Hariot entered the
service of the “Wizard Earl,” Henry Percy, the ninth
Earl of Northumberland. The Earl, who himself en-
joyed mathematical and chemical studies, established
Hariot in Sion House, near Isleworth, outside London.
There Hariot began his labors in mathematics, astron-
omy, navigation, and physics. Behind Hariot's physical
researches lay the hypothesis of atomism. As he wrote
to his friend, Johannes Kepler, Hariot advocated the
atomic doctrine as the key to natural phenomena:

(Letter of 2 December 1606,
in J. Kepler, Werke, XV, 368.)

Hariot's atomism was simple, and resembled the views
of the ancients, Democritus and Hero of Alexandria:
the universe is composed of atoms and interposed void
space; the physical qualities of gross bodies depend
upon the magnitude, shape, and motion of the constit-
uent atoms.

Hariot published nothing concerning his atomist
views; he wrote to Kepler that he could not philo-
sophize freely on those subjects. Hariot was reluctant
to make his views known because he faced a problem
which many atomists in Europe faced during the re-
mainder of the seventeenth century: atomism, with its
pagan, atheistic origins, was theologically suspect. Most
seventeenth-century thought was profoundly religious;
its scientific practitioners were not exempt from the
pious demands of the age. In order for atomism to be
acceptable as a scientific doctrine, it first had to be-
come acceptable theologically.

A third physicist who utilized the atomic doctrine,
though perhaps with more novelty, was Galileo Galilei.
Galileo is, of course, famous as the founder of the
modern science of mechanics, and as an astronomer.
His use of the atomic doctrine is less widely com-
mented upon. Galileo's Discourses concerning Two New
Sciences is the work in which he gave his most com-
plete rendering of his atomism. Written in the form
of a conversation between three interlocutors, the work
is divided into “Days.” In the very First Day, Galileo
was concerned with a discussion of cohesion, and it
is in this discussion that his atomism took shape.
Through ingenious experiments, Galileo showed that
the “force of the large vacuum” is insufficient to ex-
plain the cohesion of bodies. According to Galileo, a
vacuum in nature exerts its own force (virtù); to illus-
trate this force he described the following experiment.
If one takes two polished, smooth plates of marble or
glass and places them face to face, they will glide or
slide over one another easily, thus showing that there
is nothing between them to hold them together. But
when one tries to separate them, one finds that the
plates require a great effort to bring them apart. In-
deed, the lower one will actually be lifted into the air
by the upper! This resistance to separation, Galileo
concludes, is caused by “the aversion of nature to
empty space” (p. 11) and is present also in keeping
the parts of a solid together.

Galileo went on to measure cleverly the force of
the vacuum (forza del vacuo) by determining how
much of its own weight a column of a particular sub-
stance (e.g., water or copper) will sustain. He con-
cluded that the resistance of the large vacuum is small
in comparison to the cohesive force which binds the
small parts of a body. Why then do bodies cohere?
It is not merely the force of the external vacuum, but
rather the pressure of many tiny internal vacua which
account for this cohesion. “And who knows,” Galileo
writes, “but that there may be other extremely small
vacua which affect the smallest particles so that that
which binds together the contiguous parts is through-
out of the same mintage?” (p. 19). Although the force
of each minute vacuum is small, there are so many
of them, that their total force is significant. Some
picture of Galileo's atomism now emerges. Matter is
made up of an infinite number of infinitely small parti-
cles, interwoven with an infinity of minute vacua.
Galileo's atomism is related to the theories of Democ-
ritus and Hero of Alexandria, but is far more subtle
and far more mathematical.

It is clear that the atomisms of Beeckman, Hariot,
and Galileo are all prototypes of the mechanical philos-
ophies which would later emerge in the writings of
Hobbes, Gassendi, and Descartes. It is not surprising;
Beeckman was the mentor of both Descartes and
Gassendi; Hobbes and the others were familiar with
Galileo's Discourses. But there is a significant gulf
between the atomism of the former group and the
corpuscular philosophies of the latter. Beeckman,
Hariot, and Galileo were primarily concerned with the
explanation of specific physical problems. Galileo, for
example, was interested in the problem of cohesion;
Hariot was often occupied with the phenomenon of
refraction; Beeckman looked for the material basis for
motion, light, sound, etc. The later mechanical philos-
ophers, however, took a more systematic tack. They
were concerned with complete explanations of the
natural world, explanations designed to replace those
of their grand opponent, Aristotle. Compared to the
mechanical philosophies of Descartes or Gassendi, the
atomism of the early physicists was fragmentary, and
ad hoc.

Yet the similarities among them are important.
Beeckman, Hariot, and Galileo all were concerned with
the atheistic implications of atomism; Galileo's foil,
Simplicio, remarks on the First Day: “It seems to me
that you are travelling along toward those vacua advo-
cated by a certain ancient philosopher.” Galileo replies
through the character Salviati: “But you have failed
to add, 'who denied Divine Providence,' an inapt re-
mark” (p. 25). Later on, Descartes and Gassendi (if not
Hobbes) were concerned with ridding the mechanical
philosophy of charges of atheism. This theological
problem of atomism was one of the major obstacles
to its acceptance as a reputable natural philosophy in
the seventeenth century. How could atomism, with its
pagan, atheistic origins and implications become ac-
ceptable? This was a question which had to be an-
swered by the promoters of atomism in the course of
the scientific revolution.

There was another obstacle which became a major
difficulty barring the quick and easy establishment of
the mechanical philosophy in the seventeenth century.
This hurdle was erected by Sir Francis Bacon, and was
one primarily of methodology. Whatever twentieth-
century philosophers or historians may think of Bacon's
view of science and method, seventeenth-century sci-
entists, e.g., Robert Boyle and Hooke, regarded his
writings highly and held them in great esteem. An
understanding of Bacon's attitude towards atomism is
necessary, therefore, for the understanding of his disci-
ples in the Royal Society during the Restoration.

In Bacon's magnum opus, the New Organon (or “new
engine”), he condemned the spinning of theories, a
priori, by the Greek philosophers and their followers.
Bacon's goal in the New Organon was a novel union
of theory and practice, an examination of nature lead-
ing to secure certain axioms concerning what later
writers might call “natural laws.” His book was con-
ceived as an engine or machine to assist the mind in
discovering natural truth; the mind, left to itself, is
capable of producing only fantasies. The evil of con-
temporary philosophy, Bacon wrote in the preface, is
that it presents nature as something already known and
understood, whereas, in truth, it remains to be un-
covered and illuminated. The systematizers, or Rational
School, include both the scholastic followers of Aris-
totle and the followers of the atomists—although the
latter were more moderate in their claims. There have
been some, Bacon continued, (like William Gilbert and
his followers) who form the Empirical School of phi-
losophy. They fly up to rash generalizations merely on
the basis of a few experiments. Both the Greek philos-
ophers and the “Empirics” suffer in their natural phi-
losophies from sterility of method; neither provides a
reasonable rule of procedure to facilitate true and
certain knowledge. This rule of procedure is what
Bacon hoped to present to his readers. His method in
natural philosophy, was, simply put, the following:

(New Organon, author's preface).

Bacon was quite clear and concise; no summary
would do him justice. His goal was certainty in natural
philosophy, and his method utilized what he called an
“engine” to assist the mind and, indeed, constrain it.
Bacon sought, in general, to undermine what he called
“the mischievous authorities of systems,” and replace
them with a science founded upon orderly procedure.

A corollary of Bacon's insistence upon restraint of
the mind's fancy in science was his rejection of the
systems of the ancients—atomistic mechanism as well
as Aristotelian matter and form. The history of the
establishment of the mechanical philosophy in the
remainder of the seventeenth century can, in part, be
viewed as the reconciliation of the mechanical philos-
ophy with the methodological requirements of Baconi-
anism.

The establishment of atomism as a widely employed
scientific explanation began with the formulation of
coherent, workable systems or theories; the protago-
nists here are the French philosophers René Descartes
and Pierre Gassendi, and the Englishman (famous also
in another context), Thomas Hobbes. The story of the
acceptance and utilization of their mechanical philos-
ophies involves two major themes: the reconciliation
with Baconian methodology mentioned above and the
theological purification of the mechanical philosophy.
Hariot was made to see the dangers which mechanism
held for traditional theology; it would be the task of
later atomic philosophers to rid atomism and mecha-
nism of its atheistic taint.

It was the 1640's that marked the flowering of atom-
ism and of Cartesianism, its plenist partner in mecha-
nism. Paris in those years was the world center of
natural philosophy. Giants such as René Descartes,
Pierre Gassendi, and Thomas Hobbes were bolstered
by such talented and provocative controversialists as
Roberval, Mydorge, Mersenne, and such liberal patrons
as William Cavendish (the Earl and, later Duke, of
Newcastle) and his brother Sir Charles Cavendish. The
Newcastle Circle—including the Earl and Sir Charles,
Thomas Hobbes, John Pell, William Petty, Sir Kenelm
Digby, Lady Margaret (later the famous Duchess of
Newcastle)—was the center of British émigré interest
in the new philosophies. The Earl's table, it was re-
ported, provided a forum for discussion unmatched in
Europe.

In 1644, Descartes published his Principles of Philos-
ophy, which, though certainly not atomist in character,
greatly affected the fortunes of the atomic philosophy
both in Britain and on the Continent. The Cartesian
universe is composed of a prime matter whose essential
characteristic is its extension. Space, too, possesses
extension and consequently differs from matter only
in the imagination. Unlike the atomists, Descartes in-
sisted that matter is infinitely divisible and since space
and body are indistinguishable, there exists no “void
space” in nature. Strictly speaking, therefore, Descartes
was not an atomist but a vorticist and plenist.

The chief reviver of the atomic philosophies of
Epicurus and Lucretius was Pierre Gassendi, a French
priest, astronomer, and natural philosopher. Gassendi's

atomism was virtually an updated, Christianized ver-
sion of Epicurus. All physical phenomena, Gassendi
claimed, resulted from the diverse motions, figures, and
weight of indivisible atoms in motion through the void.
Gassendi relied heavily upon material effluvia to effect
the forces of nature in the physical world. For example,
electrical and magnetic attraction are caused by exhal-
ations from the attracting bodies of appropriate
streams of small corpuscles.

The systems of Epicurus, the pagan, and Gassendi,
the Catholic priest, have important differences. The
latter wished to exorcise from atomism the taint of
atheism. According to Gassendi, the universe requires
the existence of God who not only created it but gave
its constituent atoms a vis motrix or motive force which
provides for motion and by which Gassendi's God
regulates the world.

Both Cartesian and Gassendist corpuscularianism
exerted great influence upon atomist natural philoso-
phers on the continent and in England. The reaction
of the Newcastle Circle to these two approaches is
interesting and not unimportant. First, the group
around Hobbes and Newcastle were in large part re-
sponsible for the initial “importation” of atomism from
the continent to England in the period after 1650,
when many of the émigrés returned. Secondly, the
spectrum of atomic philosophies among the members
of the group offers an intriguing tableau of English
atomism of the Restoration period, an atomism which
was highly eclectic. On the one hand, the group in-
cluded Sir Kenelm Digby, who was one of the last
Aristotelian minimalists. He tried to link the corpus-
cular notions of Descartes, Gassendi, William Gilbert,
and others to Aristotelian natural philosophy. Digby's
smallest particles were not atoms but rather the mi-
nima divisibilia of the scholastics; he employed them,
like the modern atomists, in a quasi-mechanical way.
On the other hand, Thomas Hobbes was in the 1640's
a much more orthodox atomist.

In 1644 Hobbes, who was a close personal friend
of Gassendi, took the latter's part against Descartes.
At this time, Hobbes indicated a belief both in atoms
and in void. Had he published his major work, De
corpore, which he had already begun in 1644, at that
time, he would have shown himself on the side of
Gassendi and the atomists. However, it appeared in
print only in 1655, and by that time Hobbes had aban-
doned the vacuist position for belief in an all-pervading
aether, probably because such a medium greatly facili-
tated Hobbes' mechanistic explanations of various
forces in nature.

A good example of the similarities and differences
in the physical theories of Descartes, Gassendi, and
Hobbes can be found in their explanations of the phe-
nomenon of solidity or firmness. According to Des-
cartes, the hardness of a body is an effect of the relative
state of rest of the component particles. “I do not
believe,” he wrote, “that one can imagine a cement
more suitable to join together the parts of hard bodies
than their own repose” (Oeuvres, III, 110). Gassendi,
on the other hand, relied upon the grossness and com-
plicated shapes of the atoms of hard bodies to account
for firmness, the branches and sharp parts becoming
interlaced and making movement difficult, if not im-
possible. Hobbes relied upon motion to account for
solidity, and explained hardness as a quality which owes
its existence to the pressure of confined rapidly moving
atoms. This “kinetic theory” illustrates quite clearly
Hobbes's reliance upon motion as the instrument of
scientific explanation.

After the execution of King Charles I, the Royalist
cause began to fade, and Hobbes and the other mem-
bers of the Newcastle Circle, longing to be back in
England, returned home and brought with them the
atomic philosophy. As soon as she was established,
Lady Margaret (the Duchess of Newcastle) began to
publish her atomist poetry, and John Evelyn put out
his edition of Lucretius. In the circle of Sir Charles
Cavendish, William Petty, and the others it became
fashionable to talk among their learned friends about
the mechanical philosophy and atomism. It was in this
manner that Gassendi's atomism began to influence
English scientific thought.

Because of its pagan, atheistic origins, atomism had
always been viewed with suspicion, but now, its trou-
bles were compounded. Thomas Hobbes was also ac-
cused of being an atheist. Gassendi and Descartes,
although mechanical philosophers, were exempt from
this criticism. In their mechanical universe, Gassendi
and Descartes had made room for an immaterial, non-
corporeal Divine Being. Both of these philosophers,
moreover, admitted that man's soul, as well, is imma-
terial and spiritual. Hobbes, however, was more con-
sistent. He insisted that man's soul, in a material, me-
chanical universe, must be material. Later, he admitted
to Bishop Bramhall that even God is material and
corporeal. To all Englishmen, High Church Anglican
and Puritan alike, this was heresy; this was atheism.

In addition to its own intrinsic difficulties, therefore,
atomism had to bear the burden of having notorious
friends. Because of Hobbes, the atomists, most of whom
were actually pious Christians, were laid open to
charges of impiety and heresy. These more orthodox
atomists were greatly disturbed about the situation, and
set about to purify atomism and to dissociate it from
atheism and impiety.

Among the early opponents of the revived Epicurean
atomism were several of the famous Cambridge Pla-
tonists, particularly John Smith and Henry More.
“Epicurism,” Smith maintained, “is but atheism under
a mask” (Select Discourses [1660], p. 41). He focused
his criticism on three concepts: (1) that motion is in-
herent in matter, (2) that the soul is material and
mortal, and (3) that the world could be formed without
a Divine Architect. In 1653 Henry More published his
Antidote Against Atheism which criticized Epicurean
atomism. He objected specifically to material and me-
chanical causes for motion, and to the notion that the
complex universe could be explained without divine
intervention.

It was these objections which Walter Charleton, a
friend of the Duchess of Newcastle, a pious Christian
and a convinced atomist, tried to meet in his long
atomic treatise of 1654. This work, entitled Physiologia
Epicuro-Gassendo-Charltoniana, was designed to an-
swer the attacks on atomism and to purify it in the
eyes of believing Christians. In response to the attacks,
Charleton set about to defend atomism cleverly and
effectively. His approach was threefold. First, he tried
to demonstrate that modern Epicurean atomism was
purged of the heresies which admittedly contaminated
the pagan formulations of Epicurus and Lucretius,
specifically that the soul is material and mortal, and
that motion is inherent in matter. Charleton denied
both. Secondly, he attempted to dissociate the atomic
doctrine of Gassendi from classical atomism by joining
the attack on the atheistic aspects of it. He denigrated
what he called “this false doctrine of Epicurus” that
atoms were eternally existent and that their motion
was inherent in them. According to Charleton, atoms
were created ex nihilo by God and were infused by
Him with a motive virtue or “Internal Energy,” which
is the first cause of all natural phenomena. Finally,
Charleton tried to turn the tables on those who were
calling atomism atheistic by declaring that, so far from
being impious, atomism actually was a proof of the
existence and power of God. Who could pretend that
such a complex atomic system could come together
by the actions of millions upon millions of little atoms
alone? Some Divine Being, Charleton insisted, was
necessary for this magnificent structure.

Charleton's book was, in large measure, successful.
Over a period of several decades it was read by many,
including Robert Boyle and Isaac Newton. After
Charleton's Physiologia, almost all English atomist
works contained the pious alterations which he had
included. Moreover, it made the atomistic physics of
Gassendi readily available to those whose Latin was
weak (and these were more numerous than they ad
mitted) and to those to whom Gassendi's works were
not readily available. The purification was so successful
that even the Cambridge Platonists, especially Ralph
Cudworth, began to use a “purified” version of atom-
ism in their works.

A second, and doubtless more formidable, obstacle
to the establishment of atomism as a viable natural
philosophy was a central contradiction within its own
structure. Atomism was held to be, by its proponents,
a truer, more useful representation of nature than
opposing views—the chimerical inheritance of the
Paracelsians or the empty shell of Aristotelianism. Yet
how was this “progressive” character of atomism to
be affirmed? Neither the methodical doubt of the
Cartesians nor the empiricism of the Gassendists and
Baconians would seem to admit the highly speculative
atomic doctrine. All mechanical philosophies, orthodox
atomism included, depended ultimately upon unob-
servable corpuscles acting upon each other in ways
which had to remain inaccessible to natural philoso-
phers despite marvelous advances in instrumentation.
How was atomism (or Cartesian corpuscularianism)
to be fitted into scientific explanation?

The contradiction was recognized by the major me-
chanical philosophers, and resolved (to their satis-
faction) by recourse to a very special mode of scientific
explanation, a mode which can be described by the
term “hypothetical physics.” All the mechanical phi-
losophers—the atomists Hobbes and Gassendi as well
as the plenist Descartes—recognized that they pos-
sessed no workable method of directly observing nature
at the micro-level, and thus were prevented from
gaining real knowledge of the atomic clockwork which
to them doubtless existed. This fault, they claimed, was
fundamental to natural philosophy; “physics” at the
ultimate atomic (or corpuscular) level was inherently
barred from certitude. The certainty which all desired
(of either the Euclidean deductive or Baconian induc-
tive variety) was impossible when dealing with the
basic particles of nature and their interactions. The
natural philosopher was therefore constrained to invent
hypotheses of possible pictures of the inner mechanism
of the natural world. There were of course limitations
on these “fancies”: they had to be internally consistent
to lead logically to no obvious absurdity and finally
to be consistent with external experience. Descartes,
for example, wrote to Father Mersenne in 1638:

(trans. N. Kemp Smith, pp. 96-107).

Descartes (though not an atomist) has here provided
a new standard of scientific explanation which the
atomists would likewise agree upon. Physics of the
microworld is restricted to the invention of plausible
hidden mechanisms which must be self-consistent and
conformable to experience. Descartes (like Gassendi
and Hobbes) accepted as satisfactory scientific expla-
nations all those “Hypotheses” which satisfied the con-
sistency criteria. Naturally, there were very many such
hypotheses for any given phenomenon; competition
grew intense for the most ingenious.

“Hypothetical physics” as a mode of explanation,
though apparently forced upon atomists owing to the
limitations of their own doctrine, was modified or
rejected by the leading natural philosophers of the next
generation. Younger men, like Christopher Wren,
Robert Boyle, and eventually Isaac Newton, were
dissatisfied with what they took to be the indecisiveness
of the hypothetical physics. All retained the framework
of atomism, or a form of it, and sought new criteria
for scientific explanations and new methods to obtain
certainty in science. Atomism in the seventeenth cen-
tury could not, of course, attain the status of a certain
science; the result of these forays into new patterns
of explanation was to define the boundaries of the use
of atomism in natural philosophy.

The Reform of Atomism. The renovation of atomism
by the modification of the hypothetical physics was
a task which was Europe-wide, carried out on the
continent by scientists such as Christian Huygens
(1629-95) and in England by those natural philosophers
congregating at the Royal Society of London. The
virtuosi of the Royal Society, purporting to put into
practice (but not always with success) their motto
Nullius in verba, were uncomfortable with atomism
and with Cartesianism even after the efforts of Charle-
ton and others to purify the new philosophy. Without
question, the intellectual “patron saint” of this new
group founded in 1660 was Francis Bacon, and it was
from him that many of the members appropriated their
vision of science. [See: Baconianism.] Bacon's call for
certainty in science through experience was echoed by
his disciples in the Royal Society. The revolt against
the systematizers Descartes, Gassendi, and Hobbes
(who was excluded from the Society on several
grounds) took various forms. This spectrum of response
is usually obscured by the haste with which most British
natural philosophers assumed the too-encompassing
rubric “Baconian.” First there were the “empirics,”
who deeply suspected atomism. Like Bacon, they were
suspicious of the tenuous and hypothetical foundation
of the atomic philosophy, and though they preferred
it to Aristotelianism, they could not accept it without
serious qualifications. A typical member in this regard
was Samuel Parker, Bishop of Oxford, who wrote in
Free and Impartial Censure of the Platonick Philosophie:

(p. 46).

Parker has here laid out the major objection of the
empirics: existing theories were based loosely on a
string of conjectures with no pretense to—and what
is worse, no aspirations toward—certainty in science.
The time for theory, they claimed, is not yet ripe; what
the members of the Royal Society must do is patiently
collect data of all kinds in anticipation of the day when
theory is possible. The diagnosis of the ills of atomism
by the empirics was doubtless correct; their pre-
scription, however, led mainly to the rather uncritical
collections for which the early Society is notorious.

A second “Baconian” reaction to the hypothetical
physics of the atomists and the Cartesians can be iden-
tified with the Society's most illustrious early member,
Robert Boyle. Boyle wished to “reform” the hypo-
thetical physics by bringing it within the compass of
experimental philosophy. He was not able, of course,
to prove experimentally even the existence of atoms,
much less the truth of the hypotheses of his mentors
Descartes and Gassendi. He aimed instead at illus-
trating the ideas of the mechanical philosophers and
thereby demonstrating that, at least, the corpuscular
philosophy was conformable to experiment. In practice
the experiments which Boyle adduced were employed
by him more to discredit the Aristotelian or Spagyrical
views than to “prove” in any sense the truth of a
particular atomic or corpuscularian position. “I
hoped,” Boyle wrote, “I might at least do no unseason-
able piece of service to the corpuscular philosophies
by illustrating some of their notions with sensible ex-
periments” (Works, ed. Birch, I, 356). In the course
of this illustration, Boyle advocated what he termed
“the corpuscular philosophy,” i.e., a generalization of
atomist and Cartesian hypotheses. Boyle attempted to
depict, therefore, that a mechanical view, based upon
matter and motion, was consistent with laboratory
experience, whereas Aristotelianism and many alchemi-
cal notions were not.

A good instance of Boyle's efforts is the Experiments,
Notes, etc. About the Mechanical Origine... of...
Qualities (1675). In this work Boyle attempted to show,
in his own words, “not that mechanical principles are
the necessary and only things, whereby qualities may
be explained, but that probably they will be found
sufficient for their explication.” The qualities which
Boyle discussed were heat, cold, colors, odors, tastes,
etc. He tried to undercut the Aristotelian mode of
explanation in the case of odor, for example, in the
following fashion: he produced an odor from a non-
odorous body merely by adding water; he took two
malodorous chemicals and produced a fragrant prod-
uct; he took two bodies and produced a mixture the
smell of which was markedly different in character
from the smell of either constituent. Boyle insisted that
these changes could not have been produced by the
exchange of Aristotelian forms. His readers evidently
agreed with him, and the atomistic, mechanical view
advanced by default.

The Anti-hypothetical View. The third variety of
the “Baconian” reactions to the hypothetical physics
was more complex. There were those in the Royal
Society, who, accepting Bacon's demand for certainty
and not finding it in the hypothetical physics, empha-
sized the necessity for a more Archimedean approach:
what they called mathematics and what today might
be termed mathematical physics. The aim of this group,
which included Christopher Wren, Isaac Barrow, and,
ultimately, Isaac Newton, was primarily to forge de-
ductive theories from first principles made secure by
experiment. Instead of accepting the built-in hypo-
thetical character of physical thought about the ulti-
mate structure of matter, these men opted for the
possibility of a more rigorous approach. It should be
stressed that all were in some sense atomists; it was
their faith, unfulfilled in their lifetimes, that the atomic
motions at the root of all phenomena could be mathe-
matically described and secured experimentally.

A leader in this Archimedean-Baconian reaction was
Christopher Wren. In his 1657 Inaugural Address as
Professor of Astronomy at Gresham College, Wren
insisted that:

(Parentalia, p. 200).

What must be done in natural philosophy, Wren
claimed, is to wed the force of mathematical demon-
stration with the empirical certitude of experiment and
observation. Regarding insight into the hidden atomic
motions underlying all gross phenomena, Wren had
great hopes for future success using recently developed
and improved optical instruments.

(ibid., p. 204; emphasis added).

It is to be stressed that Wren is here directly con-
fronting the hypothetical physics, i.e., that view which
constrained natural philosophy to hypotheses “of what
Nature might be” instead of reaching, through experi-
ment and demonstration, towards certitude.

In consequence, Wren saw the aim and function of
the Royal Society as none other than “to establish
certain and correct uncertain theories in Philosophy”
(ibid., p. 197). Before the Society, Wren produced an
instrument made to represent the effects of collision
between two hard globes. By adjusting the velocity and
size of one or both of these atomic models, Wren hoped
to arrive at, in Sprat's words, “the Principles of all
Demonstrations in natural Philosophy... for all the
Vicissitudes of Nature are nothing else but the Effects
arising from the meeting of Little Bodies of different
Figures, Magnitudes and Velocities” (Sprat, p. 311).

That the mechanical laws which Wren hoped would
come out of his “instrument” were later to be laws
of atomic motion is not insignificant. It was held, im-
plicitly at least, by these last critics of the hypothetical
physics that providing a science of mechanics was the
first step in the long route around the unresolved
seventeenth-century contradiction of holding to an
atomic view and desiring certainty in science as well.

Similarly, Isaac Barrow mounted an attack on the
hypothetical physics in a fashion quite similar to the
earlier (1657) one by Wren. In a series of lectures given
in 1664-65 (English version, 1734), which Newton
attended, Barrow offered a course of action which
differed from the prevailing hypotheticalism of the
atomists and was quite similar to that of Wren. What,
he asked, do the philosophers offer but ad hoc hy-
potheses?

(Barrow, p. 61).

True science, according to Barrow, must end all
causes of disputation. The resolution of present diffi-

culties must be, not merely natural philosophy, but
mathematical philosophy.

(ibid., p. 64).

By the time Isaac Newton was prepared to enter
the scientific lists with the publication of his optical
papers (1671-72), atomism had already been estab-
lished as a viable natural philosophy. The theological
disputes surrounding its reception in the early years
had largely abated; the problem of method, particu-
larly how to justify the use of atomistic hypotheses in
an empirical way, had been papered over (not solved)
by such leading lights in the Royal Society as Wren,
Boyle and Hooke.

What was Newton's “solution”? How could Newton,
answering Barrow's call for certainty in science, like-
wise adhere to an admittedly unconfirmable atomistic
conception of nature? First of all, Newton did not
doubt the existence of atoms, but attempted to mitigate
their hypothetical character by reducing his atomism
to its barest bones and by concentrating instead upon
experimental and mathematical natural philosophy.

His famous theory of color, expanded in the 1671-72
papers, did not rest, he insisted, on any hypothesis
concerning the nature of light. As he wrote to Pardies,
“I would rather have my views rejected as vain and
empty speculations than acknowledged even as a hy-
pothesis” (Newton, Papers, p. 92), concluding, “If the
possibility of hypotheses is to be the test of truth and
reality of things, I see not how certainty can be ob-
tained in any science” (ibid., p. 106). Later he retorted
that “to examine how colors may be explained hypo-
thetically is besides my purpose” (ibid., p. 144). New-
ton best explained his position and made explicit his
rejection of the hypothetical physics, in a suppressed
part of the first optical letter. Newton wrote, in the
original: “What I shall tell them is not an Hypothesis
but most rigid consequence, not conjectured by barely
inferring 'tis thus because not otherwise or because it
satisfies all phaenomena (the Philosophers universall
Topick) but evinced by ye mediation of experiments
concluding directly and without any suspicion of
doubt” (Correspondence, I, 96-97). The discrepancy
between the manuscript and printed versions has ap-
parently unfortunately gone largely unnoticed; in it
is contained important evidence of Newton's awareness
of and reaction to the hypothetical physics.

The Principia Mathematica of 1687, though not an
atomistic work, per se, was linked to Newton's atomic
views. Much of the Principia can be, and was viewed
as presenting the mechanics of atomic motion, although
the work referred primarily to visible bodies. He be-
lieved his efforts to be applicable to atoms as well.
Rule III of the famous Rules of Reasoning in the second
edition of the Principia enabled Newton to extrapolate
from sensible experiences to understand the workings
of submicroscopic bodies. Thus, Newton was able to
state:

(Principia, Book III, Rule III).