Roger Joseph, a celebrated natural philosopher, born May 18, 1711, at Ragusa, a seaport on the Adriatic. His youth appears to have been marked by no precocity of talent while he studied grammar and philosophy in the schools of the Jesuits. Among these shrewd observers, however, his docility and obedience were sufficient to procure him particular attention. In his fifteenth year, after he had gone through the ordinary course of education, he was admitted into the order, and sent to Rome. Here his studies changed their character and direction; the rules and constitutions of the order claimed his attention for two years; after which he was instructed in rhetoric, and became well versed in general literature, particularly Latin poetry.

After completing his noviciate, he was sent to the Roman college to study mathematics and physics; and it was in these sciences that his genius and abilities shone forth so conspicuously. He soon arrived at eminence, and after being exempted from the operation of a law, by which the novices were bound to teach Latin and the belles-lettres for five years before they commenced the study of theology, he was appointed mathematical professor in the Jesuit's college. For this chair he was eminently qualified, as, besides a thorough knowledge of all the modern productions in the science, he had acquired a classical severity of demonstration by studying the works of the ancient geometers. Notwithstanding his arduous duties as an instructor of youth, it was about this Bosovich period that he formed some of those refined and original notions which were destined to grow up into the system that afterwards became so celebrated. The animating spirit of discovery and invention led him to consider every portion of physical science; and indeed so versatile and vigorous was his mind, that we should be at a loss to specify any one portion which, within a few years, it did not comprehend, elucidate, and advance. In confirmation of this it will be sufficient to enumerate the principal subjects on which he published dissertations while he continued in the professorship. These were, the transit of Mercury over the sun, the spots in the sun, the aurora borealis, the construction of spherical trigonometry, the figure of the earth, a new telescope to determine celestial objects, the ancient arguments for the rotundity of the earth, oscillating circles; on infinites and infinitely small quantities, the motion of bodies in unresisting spaces, the aberration of the fixed stars, the inequalities in terrestrial gravity; on astronomy, on the limits of certainty in astronomical observations; on the solid of greatest attraction, the cycloid, the logistic curve lines, the rives rives, the comets, light, the tides, the rainbow, the calculation of fractions, the centre of gravity, the moon's atmosphere, the law of continuity, lenses and dioptrical telescopes, the objective micrometer, and the divisibility of matter. Some of these are short, but all of them contain curious and valuable matter. It is only by perusing them that we are able to discover the gradual progress of his mind, and to understand the manner in which he arrived at that theory of natural philosophy which is now known by his name.

About this time a taste for philosophical poetry was very prevalent amongst the learned, and some of Bosovich's acquaintances had laboured in it with success. Of these we may mention Father Noceti, who wrote on the rainbow and the aurora borealis, and Benedict Stay, whose poems on the philosophy of Descartes, and on the more modern philosophy, are considered as excellent examples of Latin composition. Bosovich published the works of both with annotations and supplements which display a rich fund of information and learning. By such undertakings his fame soon became widely diffused. The learned societies of many countries in Europe conferred on him unsolicited honours, and several foreign princes invited him to their courts. His opinions on various subjects of civil architecture, topography, and hydromechanics, were solicited by Pope Benedict XIV., John V. of Portugal, and others. These applications necessarily required his presence in different states of Europe, where he never failed to enhance his reputation, and often terminated disputes which, but for his judicious interference, might have had disagreeable consequences. He was employed to correct the maps of the papal dominions, and to measure a degree of the meridian there. In this operation he was assisted by an English Jesuit named Christopher Maire. An account of their expedition was printed at Rome and Paris, and is interspersed with some curious anecdotes; but it is chiefly valuable for the detail which is given of their observations.

In 1757 he was sent to Vienna by the republic of Lucca, to settle some differences concerning the draining of a lake, in which the grand duke of Tuscany, the emperor Francis I., and that republic, were concerned; and after succeeding in the object of his mission to that city, he published there his Theoria Philosophiae Naturalis in 1758. Another occasion for his mediating powers, that more nearly interested him, soon presented itself. The British government having suspected that some ships of war had been fitted out at Ragusa for the service of France, and that its neutrality had thus been infringed, the senate of Ragusa became alarmed at the suspicion, and employed Bosovich, who had often been successful in similar missions for other powers, to proceed to London, where he effected the object of his mission,

with honour to himself; and satisfaction to his native state.

In 1760 he visited the Royal Society, which received him with distinguished marks of respect; and he soon afterwards complimented that body with a Latin poem on the solar and lunar eclipses. Boscovich was invited by the Royal Society to be of the party of their members about to proceed to America in order to observe the transit of Venus over the sun's disc; but the nature of his embassy, and the necessity of returning home, prevented his accepting the invitation. Soon after his return, he was appointed by the senate of Milan to the mathematical chair in the university of Pavia, with the superintendence of the observatory of the royal college of Brera. He continued in this situation for six years, when the empress queen appointed him professor of astronomy and optics in the Palatine schools of Milan, and also requested that he would continue to superintend the observatory. Admired by the learned, beloved by his friends, and having an adequate income, with a sound and vigorous constitution, he promised to himself much happiness in the tranquil cultivation of the sciences. But a cloud long impending now burst over his head, in the edict for the abolition of his order, which took place in 1773. No exemption from the edict could be procured; all who held offices were dismissed; and Boscovich sought refuge in Paris. Thither indeed he was invited by Turgot, through whose means he was made one of the directors of optics for the sea service, and received a pension; but he never ceased to mourn his exile, and the ruin of his order. He remained there, however, for ten years, on the expiry of which he obtained leave to visit Italy; and he published at Bassano, in five volumes quarto, a collection of the works which he had completed in Paris.

The following is a pretty accurate enumeration of their contents: A new instrument for determining the refracting and diverging forces of diaphanous bodies; a demonstration of the falsehood of the Newtonian analogy between light and sound; the algebraic formulae regarding the foc of lenses, and their applications for calculating the exactness of those which are to be used in achromatic telescopes; the causes known to be made in ocular lenses, and the error of the sphericity of certain glasses; the causes which hinder the exact union of the solar ray by means of the great burning glasses, and the determination of the loss arising from it; the method of determining the different velocities of light passing through different media by means of two dioptric telescopes; one of common, the other of a new kind, containing water between the objective glass and the place of the image; a new kind of objective microscopes; the defects and instability of a dioptric telescope proposed and made at Paris, which gives two images of the same object, the one direct, the other inverse, with two contrary motions of movable objects; masses floating in the atmosphere, as hall of an extraordinary size, seen on the sun with the telescope, and resembling spots; the astronomical reflections, with various methods for determining them; different methods for determining the orbits of comets and of the new planet, with copious applications of these doctrines to other astronomical subjects; and a method generally to geometry and to the science of calculation; the errors of rectifications, and use of quadrants, sextants, astronomical sectors, the meridian line, telescopes called transit instruments, the meridian, and the parallelistic machine; the trigonometrical differential formulae, which are of so much use in astronomy; the use of the micrometric rhombus, extended to any oblique position whatsoever; the error arising from refractions in using the astronomical ring for a quadrant, and the correction to be made; the appearing and the disappearance of the Sun's ring; methods of determining the rotation of the sun by means of the spots; the greatest exactness possible in determining the length of a pendulum oscillating every second of mean time by the comparison of terrestrial and celestial gravity; a compend of astronomy for the use of the prince, containing the elements of the heavenly motions, and of the astronomical instruments, to be explained to a prince in the course of one month; a method for determining the altitudes of the poles with the greatest exactness, by means of a gnomon alone, where other instruments are not to be had; the determination of the illuminated edge of the moon to be observed on the meridian; a method of using the retrograde return of Venus to the same longitude, for determining the less certain elements of her orbit; a method for correcting the elements of a comet, of which the longitude of the node is given, and the inclination of the orbit has been nearly found; and other matters for the same purpose, and for finding the elliptical orbit, when the parabolic one does not agree with observation; a method for correcting the elements of a planet by three observations; the projection of an orbit inclined in the plane of the ecliptic; the projection of an orbit inclined in any other plane; the calculation of the aberration of the stars, arising from the successive propagation of light; and some beautiful theories belonging to triangles, which are of great use in astronomy, reduced to the most simple demonstrations.

After the publication of these works, Boscovich quitted Bassano, and went to Rome to visit the companions of his youth. From Rome he proceeded to Milan, where he revised some of his own works, and prepared for publication the two last volumes of Stay's poems. His death took place on the 13th of February 1787, in the seventy-sixth year of his age.

Besides the different works above mentioned, Boscovich wrote several others on various subjects, as on the project of turning the navigation to Rome from Fiumicino to Macarese; on two torrents in the territory of Perugia; on the embankments of the river Ponaro; on the river Sidone in the territory of Placentia; on the embankments of the Po; on the harbours of Ancona, of Rimini, of Magna Vacca, and Savorona; besides some others, almost all of which were printed. For an account of the system developed in the Theoria Philosophiae Naturalis, see the article PHYSICS.