Dominis, Marko Antonije

(b. Rab, Yugoslavia, 1560; d. Rome, Italy, 8 September 1626)

physics.

After finishing his studies in Padua, Dominis lectured on mathematics, logic, and philosophy at Verona, Padua, and Brescia until 1596. Later he was appointed bishop of Senj and then archbishop of Split. The last years of his life were devoted chiefly to theological questions. In his main theological work, De republica ecclesiastica, which he wrote during this period and which contributed most to his fame, he urged unity of all Christian churches, their commitment to exclusively spiritual ends, and peace among nations. These beliefs made it necessary for Dominis to flee to England. Soon after his return to Rome he was imprisoned by the Inquisition. He died in a dungeon, and after his death he was found guilty of heresy and his body was burned.

Dominis had written two works on physics by the time he lectured on mathematics in Padua. The first one, De radiis visus et lucis, deals with lenses, telescopes, and the rainbow. Dominis knew how light was refracted in its passage from one medium to another, but he was not always consistent in his assertions. He held that it was possible that in some cases light could pass through the border of a medium without being refracted—for instance, into a thin layer of water. In general, his observations on refraction in lenses were correct.

After the invention of the telescope Dominis added its theoretical explanation to his work. His explanation was not entirely satisfactory, however, because his knowledge of the law of refraction was incomplete. He concluded that the image of an object was enlarged by increasing the angle of sight, which he had previously defined correctly. Thus Dominis describes in particular detail the effect on the angle of sight of a lens of greater curvature or of a greater distance between the lens and the object being viewed. With the same thoroughness he examined lens combinations, in particular the combination of a convex object glass and a concave eyepiece. This work led to his discovery of the conditions under which the magnification of an image is possible.

A greater part of De radiis visus et lucis is concerned with the rainbow. Dominis held that a rainbow is caused by refraction and reflection in raindrops: upon entering the drop, the light is refracted, then is reflected on the inner side of the drop, and then leaves the drop. This process had already been asserted by Dietrich von Freiberg, but the dependence of Dominis” theory on Dietrich’s cannot be proved. Unlike Dietrich, Dominis failed to see that upon leaving the raindrop, the light was refracted again. As for the secondary rainbow, Dominis thought that the light struck on the drops” surfaces more obliquely than in the primary rainbow. His theory does not assert that the secondary rainbow is caused after two reflections on the inner side of the drop. Dominis could not explain the order of the colors in a rainbow because he used the Aristotelian theory of the mixture of darkness and light.

In Euripus seu de fluxu et refluxu Dominis is concerned with the tides. The greater part of the book deals with the figure of the earth, advocating sphericity and refuting the opinion of Patricius, who thought that the configuration of the earth was irregular.

Dominis believed the tide was caused by the influence of the moon and the sun on the sea in a manner analogous to the working of a magnet. He adopted Grisogono’s theory of a second daily tide caused by the influence of the celestial point opposite the moon or the celestial point opposite the sun. Yielding to objections of his contemporaries, Dominis corrected this theory and introduced the influence of a transpolar circle through the moon and the sun. Dominis summed up the influences of both bodies in any position and thus accounted for all the different elevations of the sea. He was correct in believing that the tide wave was not the result of the lateral transportation of a mass of water, but rather to its rising and falling in depth and place; the wave moves horizontally, but each particle of water vertically. He wrongly ascribed the cause of tide differences in closed seas to characteristics of these seas, such as salinity and warmth.

BIBLIOGRAPHY

I. Original Works. Dominis’ scientific works are De radiis visus et lucis in vitris perspectivis et iride (Venice, 1611) and Euripus seu de fluxu et refluxu maris sententia (Rome, 1624). His main theological work is De republica ecclesiastica libri X (London, 1617).

II. Secondary Literature. On Dominis or his work, see R. E. Ockenden, “Marco Antonio de Dominis and His Explanation of the Rainbow,” in Isis, 26 (1936), 40–49; Carl B. Boyer, The Rainbow, From Myth to Mathematics (New York, 1959), pp. 187–192; Josip Torbar, “Ob optici Markantuna de Dominisa” (“On the Optics of Marko Antonije de Dominis”), in Rad Jugoslavenske akademije znanosti i umjetnosti (Zagreb), 43 (1878), 196–219; Stanko Hondl, “Marko Antonij de Dominis kao fizičar” (“Marko Antonij de Dominis as Physicist”), in Vienac, 36 , no. 2 (1944), 36–48; Žarko Dadić, “Tumačenja pojave plime i oseke mora u djelima autora s područja Hrvatske” (“Explanations of the Tides in the Works of Croatian Authors”), in Rasprave i gradja za povijest nauka (“Treatises and Materials for the History of Science”), II (Zagreb, 1965), 87–143. A complete bibliography and discussions of Dominis’ life and work (in Croatian) are in Encyclopaedia moderna, V-VI (1967), 84–140.

Žarko DadiĆ