Marci of Kronland, Johannes Marcus

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(b.Lanškroun, Bohemia [now Czechoslovakia], 13 June 1595; d. Prague, Bohemia [now Czechoslovakia], 10 April 1667)

physics, mathematics, medicine.

Marci, whose father was clerk to an aristocrat, received his early education at the Jesuit college in Juidřichův Hradec, then studied philosophy and theology in Olomouc and, from 1618 on, medicine in Prague. He took the M.D. in 1625, then began to lecture at the Prague Faculty of Medicine. He achieved considerable renown as a physician, becoming physician to the Kingdom of Bohemia and personal attendant to two emperors, Ferdinand III and Leopold I.

Although it is recorded that Marci wished to become a priest and a Jesuit, and although he took a staunchly Catholic position during the forced civil re-Catholicization of Bohemia and Moravia (1625–1626), he nevertheless represented the anti-Jesuit party in the affairs of Prague University. To gain support at the Vatican for his party’s purpose, which was to prevent the Jesuits from gaining control of the medical and legal faculties (since they already held the faculties of philosophy and theology), Marci undertook a diplomatic trip to Italy, which had important results in his scientific life. During this trip, which he made in 1639, Marci met paul Guldin and Athanasius Kircher, with whom he corresponded for a long time, and also read Galileo’s Discorsi, although he did not meet Galileo.

Marci’s political activities did not injure his career. He was professor of medicine at Prague University from about 1620 to 1660. In 1648 he took active part in defending the city against the Swedes; he was knighted for merit in 1654. He retained his academic position even after the Prague Charles University merged with the Jesuit institution to become Charles-Ferdinand University, a unification that greatly favored Jesuit pretensions. Marci became rector of the university in 1662; according to Jesuit sources he was admitted to the Society shortly before his death.

As a scientist, Marci worked in considerable isolation. The Catholic Counter-Reformation, exploited by the Hapsburg rulers, had gradually strangled scientific life in Bohemia, and access to the works of foreign scientists was severly limited. Marci’s knowledge of the researches of his contemporaries was therefore at best random, and his own work shows evidences of the ideological pressures of his own Prague environment. Marci studied many scientific subjects, including astronomy and mathematics; in the latter he was probably stimulated by the work of the Jesuit Grégoire de Saint-Vincent, who taught at Prague.

Marci’s most important work was, however, accomplished in medicine and physics. His 1639 book, De proporatione motus, contained his theory of the collision of bodies (particularly elastic bodies) and gave an account of the experiments whereby he reached it. Although these experiments are described precisely, Marci was unable to formulate general quantitative laws from them, since his results were not drawn from exact measurements of either of the sizes and weights of the spheres that he employed or of the direction and velocity of their motion. Rather, he was content with simple comparisons of the properties that he investigated, characterizing them as being “smaller,” “bigger,” or “the same” as each other; his allegations of their proportionalities are thus unproven. Some of his concepts, too (for example that of impulse), lack exact definition, but despite these shortcomings, his observations and conclusions are generally right. He was able to distinguish different qualities of spheres and to state the concepts of solid bodies and of quantity of motion.

The section on the collision of bodies in De proportione motus is only one of those in which Marci dealt in problems of mechanics. He also stated the correct relationship between the duration of the oscillation of a pendulum and its length and proposed using a pendulum for measuring short periods of time (for example, for taking the pulse of a patient). He further described the properties of free fall. Here the question of the influence on Marci of Galieo’s Discorsi must arise. The Discorsi was published a year before De proportione motus, and Marci certainly read it before publishing his own book, but the exact extent to which he drew upon it remains unknown. Certainly Marci had less skill than Galileo in reducing mechanics to mathematical forms; but if, in later years, he chose to emphasize the divergence of his opinions from Galileo’s he may well have been influenced by the attitude of the church toward the latter’s writings.

Marci also carried out research in optics, setting down most of his results in Thaumantias liber de arcu coelesti (1648). In his optical experiments, designed to explain the phenomenon of the rainbow, Marci placed himself in the line of such Bohemian and Moravian investigators as Kepler, ChristopheScheiner, Baltasar Konrád, and Melchior Haněel. In his experiments on the decomposition of white light, for which he employed prisms, Marci described the spectral colors and recorded that each color corresponded to a specific refraction angle. He also stated that the color of a ray is constant when it is again refracted through another prism (Thaumantias liber de arcu coelesti, pp. 99–100). He did not mention the reconstitution of the spectrum into white light (a result that is first to be found in the work of Newton), although he did study the “mixture” of colored rays. He also made inconclusive experiments on light phenomena on thin films. In general, Marci’s optical works are not successful in speculation, since his attempts to deduce the properties of light and to explain the causes of observed phenomena on the basis of his optical knowledge become entangled in the philosophical notions of his time.

Marci’s medical works also become involved in philosophical as well as theoretical problems. It is interesting to note that he devoted particular attention to questions of what would now be termed neurology, psychology, and psychophysiology, in treatises that have not yet been fully evaluated. His work on epliepsy is, however, worthy of special note since in it Marci tried to adopt a purely medical approach to the disease and to analyze critically both previous descriptions of epileptic fits and existing theories of their origin. From these data he drew, in obscure and symbolic terms, the conclusion that epilepsy is, in fact, a nervous disease; this result is in keeping with his theories of perception, memory, and imagination, in which his method was observational and his guiding principle that later formulated by Locke as “nihil est in intellectu quod non prius fuerit in sensu.”

It is thus apparent that philosophical considerations figured importantly in Marci’s scientific work; it is perhaps less obvious that his philosophy was in turn colored by developments in the natural sciences. Marci’s philosophy represented a sometimes incoherent fusion of Aristotelian and Platonic ideas with Catholic mysticism. From these elements he derived a speculative pantheism, based on a “world soul”—uniting the macrocosmos and the microcosmos—and a “virtus plastica sive seminalis,” or an “active idea.” He attempted to confirm his mystical beliefs by means of then newly established and often subjectively interpreted tenets of natural science; he further called upon these new discoveries to answer such philosophical questions as the relationship between mind and body and to elaborate a general view of the world and nature. (In so doing he drew close to later systems of Naturphilosophie.) Marci’s philosophical ideas probably had some influence on such Prague philosophers as Hirnheim (and perhaps even on the young Spinoza), while some of his ideas were taken up by the Cambridge platonists, among them Ralph Cudworth and, in particular, Francis Glisson.


Marci’s principal works are De proportione mouts figurarum rectilinearum et circuli quadratura ex motu (Prague, 1639), repr. in Acta historiae rerum naturalium necnon technicarum, special issue 3 (1967), 131–258; Thaumantias liber de arcu coelesti deque colorum apparentium natura, ortu et causis, in quo pellucidi opticae fontes a sua scaturigine, ab his vero colorigeni rivi derivantur (Prague, 1648; repr. 1968); Lithurgia mentis seu disceptatio medico-philosophica et optica de natura epilepsiae … (Regensburg, 1678); and Ortho-Sophia seu philosophia impulsus universalis (Prague, 1683).

Bibliographies of writings by and about Marci are Dagmar Ledrerová, “Bibliographie de Johannes Marcus Marci,” in Acta historiae rerum naturalium necnon technicarum, special issue 3 (1967), 39–50; and “Bibliografie Jana Marka Marci,” in Zprávy Čs. společnosti pro dejiny věd a technikly, nos. 9–10 (1968), 107–119.

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