Roger Boscovich and the Development of chemical Theory R. Rooney Loyola College in Maryland. Baltimore, MD 21210 Despite the influence that he had on severalgenerationsof English chemists and physicists, Father Roger Boscovich (1711-1787) remains a relatively obscure figure in the historv of chemistrv. His name is not mentioned in several works on the d j j e c ~aside ; from some journal articles and a volume ~ublishedon the 250th annivrrsarv of his hirrh ( 1 ) . little hnd ippeared about him until recently. Even now most of the attention Boscovich has received has come from his fellow countrymen in Yugoslavia and from members of the Jesuit order in which he spent most of his life. Possibly it is because of his versatility-in addition to being a physical theorist Boscovich was also a mathematician, an astronomer, an engineer, a poet, and a diplomat (I, 2)-and perhaps i t is also because his theory could not he subjected to verification a t the time, that he has been overlooked by many historians of chemistry. One could argue that the very comprehensiveness of his work on natural philosophy renders it somewhat suspect; the attempt to explain all phenomena by a single law of force is just too ambitious. Yet his influence is undeniable; a number of chemical and physical experimentalists, among them Priestley, Davy, Faraday, and Kelvin, acknowledged their debt to him. Boscovicb's ambition is understandable. He was horn at a time when the lines of various disciplines had not been firmlv drawn. This was still the are of the natural ~ h i l o s opher rather than of the scientific specialist; there was considerable breadth in the ranee of interests an investinator might have. The two great figures of late 17th century natural philsophy, Newton and Leibniz, both of whom had a profound influence on Boscovich, were as interested in theolonv as thev were in mathematics and -. and meta~hvsics . . mechanics. In addition to this general intellectual legacy, Boscovich also enjoyed certain advantages in his surroundings and his
848
Journal of Chemical Education
education. Ragusa (now Dubrovnik), his birthplace, shared in the general culture of the times; its position on the Adriatic kept it in close touch with the Italian states to the west and with the Ottoman Empire, heir to the Byzantine Greeks, t o the east. Hence the native Slavonic culture, vigorous in its own right, was further nourished through contact with Latin and Greek culture. As for education, the local Jesuit college provided Boscovich with a solid foundation in the grammar and literature of these cultures; the early training in intellectual discipline was to serve him in good stead when he decided to further his studies with the Jesuits in Rome (1,2). Boscovich entered the Society in Rome when he was fourteen. Nineteen years later he was ordained a priest. During this long period of spiritual and intellectual formation, Boscovich proved to be an apt pupil in mathematics and physica as well as in theology and philosophy. Teaching various subjects, including grammar and the humanities, further helped him to develop his intellect and to broaden his knowledge. In addition he extended his abilities in preparing a number of short treatises on topics of scientific interest; he did this, as was the custom in Jesuit schools, in Latin verse. I t was while he was studying mathematics that Boscovich came across the works of Newton. This encounter was to prove remarkably fruitful. In the next few decades Boscovich would take the basic ideas set out in the Queries appended to Newton's "Optics" and synthesize them with the physical theories of Leibniz. I t was this synthesis, yielding the single law of attractive and repulsive forces acting hetweenpoints, that was tomake such an impressionon Priestley and succeeding generations of chemists. Although the full exposition of these ideas on natural philosophy was not presented until 1758 in the "Theoria," elements of the theory are found in Boscovich's letter and some of his shorter treatises published during the 1740s, most notably the "De Viribus Vivis" (1745). One can truly say then that although
Boscovich had many other accomplishments to his c r e d i t observations on sunspots, studies on geometrical propositions, contributions to the design of optical instrumentshis maior work was the theorv of a single law of forces. ~ h e " ~ h e o r i a "resulted from his consideration of a basic nrohlem in nhvsics: findine the center of oscillation of three bodies. f he Gestion wasposed by a Jesuit colleague, Fr. Scherffer; Boscovich, in answering his friend, took the opportunity to develop a t length ideas he had been considering for some time. His point of departure in tackling the problem of collisions was Leibniz's "law of continuity"-"nothing occurs in jumps"-an observation that Boscovich wholeheartedly accepted. Using this law Boscovich argued that in the collision of two indivisible bodies their velocities ahould not change instantaneously hut, instead, gradually. Otherwise one would he led to the absurd conclusion that a body could have, a t the moment of collision, two different velocities: Suppose there are two equal bodies, moving in the same straight line and in the same direction; and Let the one that is in front have a degree of velocity represented by 6, and the one behind a degree represented by 12.. .at tbevery instant of time at which. . .contact haonened. .. the hindermost bodv should diminish its velocity, and the foremost hody increase its velocity, in each case by a sudden change.. . .. .if in the whole time before contact the anterior surface of the hody that follows had 12 degrees of velocity and in the subsequent time had 9.. .a sudden change being made at the instant that separates the two times, the body would be bound to have 12 degrees of velocitv, and 9, at one and the same time. This is absurd.. .(3) However, to account for this gradual deceleration, i t was necessary to posit the existence of repulsive forces acting a t very close distances. The suggestion of forces acting at a distance Boscovich had come across in Newton; where he differed from Newton was in postulating that at very small distances these forces must he strongly repulsive and not attractive. . forcea are rrpulsive at very small distance$and become indefinitrly greater and greater, na the dirtancer art. diminishrd ind~finitely, in such a manner that they are capable of destroying any velocity (3). ,.
A logical implication of this law of force is that there is no contact between bodies in a collision. Ironically, then, by adhering resolutely to the law of continuity, Boscovich disclosed a fundamental discontinuity a t the heart of nature. Here he narted wav with Leibniz. who had insisted that there must he continuous extensionin matter ( I ) . Boscovich preferred to make the simplest assumption possible about fundamental bodies in nature: they have no extension and no mass whatsoever. As he explained in the Theoria: The primary elements of matter are, in my opinion, perfectly indivisible and nan-extended points.. .matter is interspersed in a vacuum and floats in it. . . . There is absolutely no argument that can he brought forward to prove that matter has continuous extension, and that it is not rather made up of perfectly indivisible points (3). In this scheme "atoms" or "basic units of matter" were reduced to "point atoms" or "centers of interaction." Direct contact between these atoms was nrevented hv a repulsive force; however, a t greater distances the repulsive force would diminish and be succeeded hv an attractive force. Renulsive and attractive forces would alternate; a t certain distances where neither the attractive nor repulsive forces operated the arrangements of point atoms would he stable. The continuous curve extending from the ordinate in the diagram below represents qualitatively the forces governing the interactions between two point atoms. For any point lying ala,verhex-axis the f#grceisrepulsive;atvery shoit distances the repulsive forces increases indefinirely.
ATTRACTIVE
For any point lying below the x-axis, the force is attractive. As the distance becomes ereater and greater. the force law approaches the inverse square law established by Newton. By allowing the point atoms t o assume a variety of different arrangements, Boscovich was able to aecount for the existence of different substances. Although the point atoms were identical, once they were combined into larger particles, different relationships with other points would he possible. This theory of fdrces, when Gesented in full in 1758, received considerable attention partly because Boscovich had already established his reputation in several areas and partly because similar ideas had been suggested by other theorists. Kant, for example, had presented in 1756 arguments similar to those of Boscovich; during the early '60's a young English astronomer, John Michell, who was shortly to become acquainted with Joseph Priestley, arrived independently a t the idea of immaterial point atoms ( I ) . Another reason for the general receptiveness to the theory was its simplicity and logical consistency. Boscovich had reduced all particles to a single type, and he had made that type featureless. Furthermore the laws governing the interactions of particles had been reduced to essentially one as well. The theory allowed one to explain, with great economy, a great many natural phenomena: the states of matter, cohesion, elasticity, and crystallization, to name just a few. For example, Boscovich accounted for cohesion quite simply: i f two mints are at the distance thatcorres~ondst o that of anv of the limit-points[in which the curve of forces cuts the axis],and the forces that arise when the distances are changed are great enough.. .then the points will maintain this distance apart with a very great force;so that when they are insensibly compressed they will resist further compression,and when pulled apart they resist further separation. . r - ~ - ~ ~ - - ~ - ~ ~~~
~~~~
~~~~~~~
~~~
~
~
It would proveappealing to chemistri in future years bpcause
it brought order to thr subiect at a time when the numher of elemen& was rapidly increasing. Following the publication of the first edition of the "Theoria," Boscovich made several trips, one to Paris in 1759 and one to England that lasted for seven months in 1760. He met with many members of the scientific community during his visit, among them Michell, then a t Cambridge. I t is known from Boscovich's correspondence ( 1 ) that he talked with Michell; possibly this meeting encouraged Michell to pursue further thinking on the theory of immaterial atoms. At any event Michell told Priestley about Boscovich's ideas as well as about his own several vears later when Priestley was preparing his manuscript un&tirs (..The Historv and Present State of 1)iscoveries Relating to Vision, ~ i g h t and , Colours") (1,4). These speculation~apparently appealed to Priestlev, because he included them in his dis.. cussiun of the penetration uf matter by light; Boscovich he praiwd as "one uf rhe first rate mathemnticians and phiiosphers of the present ege" (5). Perhaps of equal importance to Priestley was that the nature of matter outlined in the "Theoria" could also he used to support his own eccentric theological system in which the soul is reduced t o a type of matter (point atoms) (1,6). Several of his metaphysical works show him employing Volume 62 Number 10 October 1985
849
the theorv in iust this wav: it was. in fact. this use of the theory that led to an angry exchange of letters between Boscovich and Priestlev in 1778 and to an end of the contact between the two that h i d begun four years earlier when they had met in Paris. Although Priestley's later scientific works do not contain any explicit references to Boscovich, there are a number of placesin his writings where Priestley appears to be relying upon the point atom theory as a conceptual framework (I). For example in aletter to his friend Josiah Wedgewood there is a passage in which he discusses the separation of water into it components: I had also a general idea that if the parts of any bodies be rarefied beyond thesphere of attraction they will beinasphereof repulsion to each other (6).
In the treatise "Experiments on the Generation of Air from Water," written in 1793, Priestley expressed quite openly a belief that it is the arrangement of fundamental particles in different ways that gives rise to the different elements:
.. . the advances we are continually making in the analyses of natural substances into the elements of which they consist, bring us but one step nearer to their constitutional differences; since as much depends upon the mode of arrangement, concerning which we know nothing at all, as upon the elements themselves. Far things the most different in their properties appear to consist of the very same elements ( 6 ) . These ideas on the importance of structure in chemistry and on point atoms as the basis of that structure received a much wider hearing ten years later with the publication of Thomas Thomson's "System of Chemistry." Thomson was by no means convinced of the theory as was Priestley; nevertheless, he set down the basic postulates carefully and showed how alternating spheres of attraction and repulsion could account for many physical phenomena. He accepted Boscovich's conclusion that there is no contact between the fundamental particles: Baseovich has demonstrated, that a body in motion communicates part of its motion to another body before it actually reaches it. Hence we may conclude that, as far as we know, there isnosuch thing as actual contact in nature.. .(7). Thomson had particularly high regard for Boscovich's treatment of cohesion: The nature of cohesion has been more happily explained by Boscovich than by any other philosopher. Indeed it forms the most beautiful and satisfactory part of his theory (7). Boscovich's theory was also discussed in the course of nublic lectures on chemistrv eiven in 1801 bv Thomas Garnett a t the Royal 1nstitution.Carnett2stalksUmayhave been the first occasion on which his young assistant, Humphry Davy, had encountered this new way of thinking about matter (8). Davv was urobablv alreadv a convinced atomist a t S iecturesBt the ~ b ~Institution-he a l sucthe time. H ~ own ceeded Garnett as professor there in 1802-show him as distinctly opposed to the positivist outlook of Lavoisier. Where the latter was unwilling to go beyond the limits of chemical analysis in defining elements, Davy was willing to speculate on the ultimate structure of matter: The different bodies in nature are composed of particles or minute oarts. individuallv imoerceotibleto the senses. . .the chemical are repulsion, or the agency of heat, and attraction (8).
Ironically, Davy was to extend the number of elements known even further through his eh?eriments with electrolysis and his discovery of chlorine and iodine. He insisted, nevertheless, that the number of fundamental particles 850
Journal of Chemical Education
must he small; on the basis of observed simplicity in nature he argued: Whoever compares the complication of the systems which have been adopted, and the multitude, as it were, of insignificant elements, with the usual simplicity and grandeur of nature, will surely not adopt the opinion, that the highest methods of our science are already attained. .$3). One can see in this his strong faith in the unity of matter; if one probed deeply enough, that unity would be found. Davy's position was bolstered by his finding that graphite and diamond, two substances as different in properties as one could find, are one and the same element. Boscovich's theory, unlike Dalton's atomism, could explain the difference in properties on the basis of structural dissimilarities; consequently, Davy was to adopt it as a theoretical framework for understanding chemical phenomena. Two years after publishing his "Elements of Chemical Philosophy" (1812), in which he described Boscovich's theory, he jotted down the following observation: By assuming certain molecules endowed with poles in points of attraction and repulsion as Boscovich has done, and giving them gravitation and form, i.e., weight and measure, all the phenomena of chemistry may be accounted for (8). Although in the last decade of his life Davy was less and less involved with research, he continued to speculate upon the nature of matter. His posthumously published "Collected Works" include a dialogue between a natural philosopher and several interlocutors. One passage in particular indicates that Davy fully accepted Boscovich's ideas: .. . I do not suppose the elements to be physical molecules endowed with the properties of the bodies we believe to he undeeomposeable.. .I consider them, with Boscovich, merely as paints possessing weight and attractive and repulsive powers; and eomposing according to the circumstances of their arrangements either spherules or regular solids, and capable of assuming either one form or another (9). Insupport of this view Davy could adduce several pieces of evidence: the sharp melting points of solids, the crystallization of materials in regular polyhedral structures (9), the liquefaction of gases heated under pressure (10). In Dalton's atoms were view. to which Davv was verv much ouoosed. .. hardmassy spheressurrounded by caloric; transitions from one phase to another would not he ahrunt but instead eradua l as hear expanded the mlnric; aggre&rion would reiult in tht: formation of irregular clumns; hrntina would dri\.e oarticles further from one anothe; and m a i e association that much more difficult. In the Boscovichian system sharp phase transitions could be explained as the result of a rapid jump from a sphere of attraction to a sphere of repulsion: &y&allization&dd be expected to occir in ordered arrays because of the pattern of force fields surrounding particles: heating a gas under pressure could lead to the&ssage of point atoms from a sphere of repulsion to a sphere of attraction at a greater distance. In Davy's mind, then, the Boscovich theory accounted for a number of chemical phenomena; a t the same time it uossessed a wonderful simolicitv. Davy's ideas prdhahly had a powerful influence on his young protege, Michael Faraday. Faraday had attended lectures by Davy a t the Royal Institution in 1812; the following sear he became Daw's assistant. At Davv's suaeestion Faraday carried out the-experiments on liq;efyinggases under pressure; he also helped Davy in revising the "Elements of Chemical Philosophy." By this time the inadequacy of the Daltonian model of the atom must have become apparent to Faraday (10). Faraday, though, was cautious in adopting theories or in making generalizations on the basis of a few laboratory results. Consequently, his earliest lectures, given when he was still an assistant, indicate that while he could see the objections to Dalton's scheme of things, he was not yet ready to embrace Boscovich's theory:
. ..the attractive power which all the particles of matter possess one on another is not sufficient to account for them for this power would cause them to combine indiscriminmtlv and without anv trndency rurertain partirolarsir~~nri~n~. . .the pnrtdesoimatter aredcrrtain dcfinitcnnd similar iorms.. .thpip pnrriclei.. unite only in particular positions, certain sides of the particles always coming into contact. This however can only be explained by supposing a polarity to exist in the particles and that certain points attract whilst others repel. . .(lo). ~~~~
~
There is a t least a n implicit acceptance here of the system of alternating repulsive and attractive forces, hut the nature ihemselves is left quite vague as Faraday's of the biographer, Pearce Williams, has pointed out. Faraday seemed to he more sure of what they could not be than of what they are. He did include, however, a brief reference to point atoms:
. . . but a theory has been started, which supposes matter to he merely a collection of mathematical points of attraction, and repulsion; and these points having no parts, it is said that they have neither extension or solidity; and that, if it were possihle to overcome the repulsive and attractive forces, two portions of matter might coexist in the same place (10). 111the course of his subsequent investigations intoelertroniagnetir phenomena, dntin: from 1XX onward, Faraday found himivlt' drnwn more and more toward the Roscuvirhian conception of the atom. With point atoms arranged in pnrtivulnr fashions m e n d l rationalize the pattern of magnetlc and electrical lines of tlme as well as those of rhemiral arrinitv. The Hosco\.ichian ntom offered the further attraction of requiring the fewest number of assumptions about small scale structure. However. it took more than two decades for Faraday to commit himself puhlicly to point atoms. In his DaDer "A S~eculationTouchine Electric Conduction and the Gature o F ~ a t t e r , "Faraday p;esented the following sketch of atomic phenomena:
. . . i f . . .two atoms he centres of power they will mutually penetrate to the verv centres. thus formine one atom or molecule with A number of scientists had objected that Boscovichian point atoms could not serve as the basis for a real world since they lacked mass. Faraday answered by pointing out that in relation to the distances across which the most far-reaching and most widely accepted forces (i.e., gravitational forces) operate, the masses involved are little more than point atoms (8). Several contemporaries of Faraday were also influenced by Boscovich's theory. Although he himself did not adopt the theory, John Daniell, professor of chemistry a t King's Colleee. London. and inventor of the hatterv cell that hears his ll.imr. did at lr:i.;t give it some consideration. The second edition of his "Introduction to the Srud~oiChemiraIPhilosophy" (1843) deals with point atoms asbell as with the hard, massy spheres of Newton. Around the same time the noted mathematician, Sir William Hamilton, defended the theory of repulsive and attractive forces acting between points in a talk he gave a t the British Association. He did not mention Boscovich by name, but the ideas he championed were unmistakablv those of Boscovich (11). ~ i l 1 i a m " ~ h o m s o(later n ~ o r ~dk l v i u )possibly , as a result of his work withFaraday on electrostatic theory, also took an interest in point atoms. His attitude, on the whole, can only he described as ambivalent. Early in his career he favored the theory, hut he abandoned it around 1860 when he hit upon the idea of atoms as vortex rings (8.12).Unfortunatelv. the new theory suffered from the same flaw as the old one; neither could account verv well for mass or inertia. Consequently, in 1889 he was, if not promoting the Boscovich atom, a t least using it, in this case to determine the equilihrium for groups ofatoms. He also took the occasion to ac-
knowledge rhe utility of point atoms in tackling sttch problems as the elasticity of solids (e.g., the work of Navier and Poisaml and the kinetic theory of gases (e.g., the studies of Maxwell, Clausius, and Taitj (13).In later papers he continued to employ Hoscovichian assumptions even though he wns never ftllly ronvinred of the point atom's reality (1.1). A find example of Boscwich'r influence among chemists is fuund in J . J. Thomson'a "Corpuicular Throry ot' Matter," published just a iew years before Rohr presented his ideus on atoniicstructure (1.15~.'Thornson, in discussing. the possihility that corpuscles (i.e., electrons) orbit the ceitralion (i.e., the nucleus) in fixed paths, employs the Boscovichian theory as a model: Suppose we regard the charged ion as a Boscovichian atom exerting a central force on a corpuscle which changes from repulsion to attraction and attraction to repulsion several times between the surface of the ion and a point at a distance from the surface comparable with the molecular distance. The condition that the circular orbit should he stable.. .will only he satisfied at parts of the Boscovichian curve. . .
It is a tribute to Boscovich's power of mind and his devotion to work that his theorv survived for so lone. As several commentators have ohseried, his concept was developed independently of any quantitative work; for the most part i t rested upon general-observations and close reasoning. Nevertheless, i t suggested a program of research for several chemists; for that alone it is worthy of attention. Although with the publication of the "Theoria" Boscovich has comnleted his ereatest work. he continued to oursue various projects with vigor. In 1764 he became professor of mathematics a t Pavia. where he undertook the revitalization of the university; a t nearby Milan, which he often visited, he supervised the construction of an up-to-date observatory. These and other tasks he accomplished amid the troubles caused by health ~ r o h l e m spersonal , disaereements. and the t ~ v e with n the kppresgrowing attacks on the ~ e s u iorder. sion of the order in 1773 and his relocation in France, Boscovich did not relax, devoting himself to researches on the telescope and revisions of his publication on eclipses. Finally, though, his health deteriorated even further; he returned to Italy and died there in 1787. One of his friends said of Boscovich that he possessed the qualities of a great man, and even those who disagreed with him could hardly deny his genius. Perhaps in the future his work will receive more of the attention from chemists that i t so richly deserves.
-
Literature Cited (1) Whyte, L. L. (Editor), "Roger J n a p h Bosmvich Fordham University Press. N e w York, 1961.On Bncovich's lifesoe Hill. Elizabeth. "Roger Bmovieh: A Biographical Essay," pp. 17-101; on his work see Why*. L. L., "Bneovieh'sAtomism: pp. 102-126 and Markovi~,Zeljko, "Bascovich's Theoria'," pp. 127-152. For B n e o ~ vich's influence on chemists see wi11iama..I Pear% "Bosmvieh and the British Chemists..) pp. 153-167and SehoFleld, Roben E., "Bascovich and Priestley'aTheory of Matte,."pp. 16G172. (2) Keo8an.F. E.. TheMonth,20,340(1958): 0'Conneli.D. J. K.,Sludis. 51,487 (19621. (3) Bosovich, S. J., Roger Jneph."Theoryof Natural Philosophy: (trans.: Child, J. M i . MIT Press, Cambridge. MA, 1966. (4) Geikie, Sir Archibald, "Memoir ofJohn Mieheil: University Press, Cambridge. 1918. (a ~ ~ i ~ ~ t ~ ~ present ~ . state ~ ~ of~iscovpries ~ ~ ~ ti^^ h , fo-vision, ~ ~ i i ~~ h tt , ~ and Colours," printed for J. Johnson, London, 1772, (6) Schofield. Robert E. (Editori, "A Scientific Autobiography of Joseph Priestley, 17331SO1.1.MIT P r e s Cambridge, MA, 1966. (7) Thomsun. Thomas. '"A System of Chemistry in Four Volumes: from the 5th London edition. with notes. hy Thomaa Cwper; A. Small, Philadelphia. 1818. (8) Knight. David, M., "Atoms snd Elements: Hutchinson, London, 1967. (9) navy, Sir Humphy, Coileef~dWorks. (Editor: navy, John). Smith Elder & Co.. Loodon, IMO, V d . 9. (1Oi Williams, L. Pearco."Michael Feraday,"Baaie Books, New York, 1965. (111 Sutton. M. A.,"Studie~in the History and Phil-phy of Science? 1,277 (1971). I121 Silliman,Robert H.,1&,54,461 (19631. (131 Kelvin, Baron, (William Thomronl Smithranion lnsliflrfion Annuoi Reports, 435 (18891. (141 Thompson, S. P., "The Life af William Thomson, Baron Kelvin of Lsrgs: MacMilIan. Landon, 1910. (161 Thomson. J. J., "The Corpuscular Thaory of Matter: Archibald Constable and co.. London, 1907.SeealsoCilt.S.J., Henry V.,"RogerBneovieh,S. J.: M. H. Gilland Son, Dublin. 1941.
Volume 62
Number 10
October 1985
85 1
~
~
