Astronomer, b. at Reggio in Emilia, Italy, 18 June, 1818; d. 26 Feb., 1878. He was the son of a joiner, Antonio Secchi. His mother (née Luise Belgieri), a practical middle-class woman, had her son taught even sewing and knitting. After studying for several years in the gymnasium kept by the Jesuits in his native town, Secchi in his sixteenth year entered the Jesuit Order at Rome on 3 Nov., 1833. After completing his humanistic and philosophical studies at the Roman College, on account of his extraordinary talent for the natural sciences he was appointed tutor of mathematics and physics at Rome in 1839, and professor of physics in the Jesuit college at Loreto in 1841. In the autumn of 1844 he began the study of theology under the most distinguished professors (Passaglia, Perrone, Patrizi, Ant. Ballerini ), and on 12 Sept., 1847, was ordained priest by Mgr Canali. At the outbreak of the Roman revolution in 1848, he had to leave Rome with all his fellow- Jesuits. Accompanied by his teachers, de Vico and Pianciani, he travelled first through Paris to England, where he resided for a short period at Stonyhurst College. On 24 Oct., 1848, he sailed with twenty other exiled Jesuits from Liverpool to the United States, which he reached on 19 Nov. Secchi's companion, de Vico, renowned as the discoverer of several comets, had succumbed in London to typhus fever contracted in consequence of the hardships of the journey, and in death was honoured in an enthusiastic notice by John Herschel in the "Monthly Notices of the Astronomical Society ". Secchi settled in Georgetown, near Washington, District of Columbia , where the American Jesuits conducted a university and an observatory (then under the care of Father Curley ). Here he brought his suddenly interrupted theological studies to a close by a brilliant examination for the doctorate, and joined the faculty of the university as professor of physics. Astronomy as yet claimed little of his attention, as ho wished to perfect himself as a physicist. Of decisive importance for his later achievements in the domain of meteorology was his close friendship with the celebrated hydrographer, meteorologist, and astronomer, M.F. Maury, who lived in Washington. To this friendship, through the medium of Secchi, Italy owed its first acquaintance with the epoch-making discoveries of the great American, whose valuable services in marine meteorology and navigation cannot be overrated. In later years Secchi dedicated to his friend, "as a token of our mutual friendship", his work, "Sui recenti progress! della Meteorologia" (Rome, 1861), and on his death in 1873 gave him an enduring memorial in a warm and touching necrology (cf. "Bullettino meteoroloigco del Collegio Romano", XII, Rome, 1873). Contrary to expectation, Secchi's residence at Georgetown soon came to an end, when the Roman revolution was forcibly terminated by the French general, Oudinot. On 21 September, 1849, he had to begin his return journey to England, and in 1850 he undertook the direction of the observatory in the Roman College, for which post his teacher de Vico had warmly recommended him on his death-bed. Because of the instability of the foundation walls and the want of modern instruments, Secchi was at first (1850-52) compelled to be content with his investigation concerning the radiation of the sun, the rings of Saturn, and the planetoids. By the end of 1852, however, his energy had succeeded in having a new observatory prepared on the firm vault of the Church of St. Ignatius in the Roman College, and fitted with new instruments. From this time date Secchi's brilliant scientific activity and the European fame of his observatory. On account of the extraordinary variety of his investigations, we must distinguish three persons in Secchi; the astronomer, the meteorologist, and the physicist.
As an astronomer Secchi began with a revision of the great catalogue of the double stars made by W. Struve at Dorpat (1824-37). After seven years of strenuous labour he was able to print the chief portion of his results in the "Memorie del Collegio Romano" (Rome, 1859) with 10,000 verified double stars; this was continued in two supplements, published by his assistant in 1868 and 1875. One of the best calculators of the courses of the double stars, the astronomer Doberck of Dublin, has to a great extent taken Secchi's catalogue as the basis of his calculations. Hand in hand with this gigantic task went his study of the physical conditions of the planets Saturn, Jupiter, and Mars, and of the tour great moons of Jupiter. On the discovery of spectrum analysis by Kirchhoff and Bunsen (1860), Secchi was the first to investigate closely the spectra of Uranus and Neptune. From 1852 the moon also became the subject of his investigations. He made so exact a micrometrical map of the great crater of the moon (Copernicus) that the Royal Society of London had numerous photographic copies made of it, and had them distributed among those interested in astronomy. All Secchi's studies on the planets were included in his great work, "II quadro fisico del sistema solare secondo le piu recenti osservazioni" (Rome, 1859). However, the chief object of his study was the sun, with its wonderful faculae and spots, to which he devoted from the very beginning his incessant attention, industriously registering his observations. Epoch-making for the study of the sun was his expedition to Spain to observe the total eclipse of 18 July, 1860, because by him and his fellow-observer it was first definitively established by photographic records that the corona and the prominences rising from the chromosphere (i.e. the red protuberances around the edge of the eclipsed disc of the sun) were real features of the sun itself, and not optical delusions or illuminated mountains on the moon. When, on the occasion of the eclipse of the sun of 18 August, 1868, the French astronomer Pierre Janssen demonstrated practically the possibility of studying the protuberances even in clear daylight by certain manipulations of the spectroscope (this had been independently shown in theory by Norman Lockyer in London ), Secchi was one of the first to keep a regular diary of all phenomena connected with the protuberances and of all other data concerning the physics of the sun. He thus laid the foundation of the unique "Sun Records", which have been continued to the present day; no other observatory in the world possesses a work of this character which has been kept so long (cf. Millosevich, "Commemorazione del P. Secchi" Rome, 1903, p. 20).
Secchi also took part in the Italian expedition to observe the eclipse of the sun on 22 Dec., 1870, in Augusta, Sicily. Although his observations were not favoured by the weather, he was repaid for this journey by the discovery of what is called the "flash spectrum" which is considered a direct proof of the existence of a "reverting stratum" ( "umkerenden Schicht" ), a mixture of glowing metal vapours which lies over the photosphere and by its elective absorption produces the dark Fraunhofer lines in the sun's spectrum. During this same eclipse Professor Young of the American expedition saw clearly in his spectroscope the bright lines of the flash spectrum. Secchi published the results of his own investigations and those of others in a French work long regarded as standard: "Le soleil. Expose des principales découvertes modernes" (Paris, 1870). The second appeared in two volumes as an edition de luxe (Paris, 1875-77), after the German translation by Schellen had appeared under the title "Originalwerk bezuglich der neuesten vom Verfasser hinzugefügten Beobachtungen u. Entdeckungen" (Brunswick, 1872). In the study of the fixed stars Secchi distinguished himself not only by the invention of new instruments (heliospectroscope, star spectroscope, telespectroscope), but especially by the discovery of what are known as the five Secchi types of stars deduced from about 4000 spectra of stars, on which he had been at work since 1863. The unexpected discovery that all fixed stars may, according to their physico-chemical nature, be reduced to a few spectral types, was an achievement of as great significance as Newton's law of gravitation. This great law was confirmed by the works of d'Arrest of Copenhagen and E. C. Pickering of Harvard (in his well-known "Draper Catalogue"). When H. C. Vogel of Potsdam (1874) changed Secchi's purely empirical division of the stars into a genetic development of the stars from type to type, the theory of the unity of the world and of the identity of the fixed stars and the sun received most profound scientific demonstration and confirmation. Secchi published his views concerning the world of stars in "Le Stelle" (Milan, 1877), which appeared in German as the thirty-fourth volume of the "Internationale wissenschaftliche Bibliothek" (Leipzig, 1878). Passing over his other investigations concerning comets, groups of stars, and nebulous stars, we may remark in passing that Schiaparelli's celebrated treatise on the relations between the groups of asteroids and comets was published in Secchi's "Bullettino meteorologico" (Rome, 1866).
As a meteorologist, Secchi was, as already said, an enthusiastic disciple of the American M.F. Maury, whose discoveries he utilized and continued with uninterrupted zeal throughout his life. He turned his attention to the most varied phenomena, e.g. the aurora borealis, the origin of hail, of quicksand, the effects of lightning, the nature of good drinking water, etc. He was the first to ascribe, on the basis of ingenious experiments, the telluric lines of the spectrum of the sun to the influence of atmospheric vapour. Secchi especially studied the "Roman climate". Still greater interest for him had the investigation of terrestrial magnetism and terrestrial electric currents. He was the first to organize a systematic observation of these currents as an eventual means of prognosticating the weather, and worked with good results in union with other observatories with similar aims (e.g. Greenwich, England ). The Magnetic Observatory, arranged and fitted by Secchi in 1858, was for a long period the only one in Italy. Commissioned by Pius IX, who promoted all his undertakings with princely liberality, he made long travels through France and Germany in 1858 to procure the most suitable projection lenses for the lighthouses of the papal harbour towns. He secured, however, his greatest fame by his invention of the "Meteorograph", a skilfully-constructed weather machine, which works day and night and records the curves of atmospheric pressure, temperature, rainfall, rainy season, . strength of wind, and relative dampness of the atmosphere. In its original form the "Meteorograph" was extremely simple, but in 1867, through the munificence of Pius IX, it received a magnificent case, and in this form claimed the admiration of everybody at the Paris Exhibition of 1867. It created a great sensation, and Secchi received as prize of honour from the hands of Napoleon III the large gold medal and the insignia of Officer of the Legion of Honour ; from the Emperor of Brazil he received the Order of the Golden Rose. An exact description of the apparatus with illustrations is given in the brochure, "II meteorografo del Collegio Romano" (Rome, 1870).
As physicist Secchi was a disciple of Piancini, and devoted himself from the beginning preferentially to astrophysics, then to a great extent regarded as of secondary importance. American readers will be interested to learn that Secchi contributed one of his best works on "Electrical Rheometry" to the "Smithsonian Contributions to Knowledge", III (Washington, 1852). If we may include in physics geodetic measurements, the calculation of the trigonometric basis on the Appian Way for the future triangulation of the Papal States especially deserves honourable mention. By discharging this tedious and difficult task on the commission of the papal government between 2 Nov., 1854, and 26 April, 1855, he supplied one of the most important fundamental data for the subsequent gradation of Southern Europe. His results were edited in model fashion in the great work, "Misura della Base trigonometriea eseguita sulla Via Appia" (Rome, 1858). He acquired world-wide fame as a physicist by his greatly-admired work, "Sulla unitá delle forze fisiche" (Rome, 1864), which attempts to trace all natural processes to kinetic energy. With astounding acumen he here combines in a uniform picture all the results of earlier natural science, and anticipates and even in certain ways outstrips later investigations and views. The second edition (2 vols., Milan, 1874) was translated into French, English, German, and Russian. Secchi was, however, too much of a philosopher and a Christian to venture, after the fashion of more modern Materialists and Monists, to extend his "kinetic atomistics" to the domain of the soul and the intellectual. On the contrary, his whole natural system was founded on a theistic basis, inasmuch as he traced back the world of matter and its motion to a Divine creative act. In two magnificent lectures, which he published at the beginning of his "Lezioni elementari di fisica terrestre" (Turin and Rome, 1879) and independently in a German translation by Dr. Güttler (Leipzig, 1882; 4th ed., 1885), he gave a more than eloquent expression to his Christian view of life. After the capture of Rome by the Piedmontese in 1870, his firmness of faith and his fidelity to the pope and the Jesuit Order were more than once put to a rude test. But no enticements, however alluring, of the new rulers (e.g. the general supervision of all the observatories; the granting of the senatorial dignity with express release from the constitutional oath ) could induce him to falter in his loyalty or fidelity. The new authorities did not venture to expel him from his laboratory, and he continued his investigations until he succumbed to a fatal disorder of the stomach.
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