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 SECCHI

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SECCHI

Secchi also took part in the Italian expedition to observe the eclipse of the sun on 22 Dec, 1S70, in Augusta, Sicily. Although his observations were not favouied by the weather, he was repaid for this journey by the discovery of what is called the "flash sp>ectrum" which is considered a direct proof of the existence of a "reverting stratum" {" umkercndcn Schicht"), a mixture of glowing metal vapours which bes over the photosphere and bj^ its elective absorp- tion produces the dark Fraunhofer lines in the sun's spectrum. During this same eclipse Professor Young of the American expedition saw clearly in his spec- troscope the bright lines of the flash spectrum. Secchi published the results of his own investiga- tions and those of others in a French work long regarded as standard: "Le soleil. Expose des prin- cipales decouvertes modernes" (Paris, 1870). The second appeared in two volumes as an edition de luxe (Paris, 1875-77), after the German trans- lation by Schellen had appeared under the title "Originalwerk beziiglich der neuesten vom Verfasser hinzugefugten Beobachtungen u. Entdeckungen " (Brunswick, 1872). In the study of the fixed stars Secchi distinguished himself not only by the inven- tion of new instruments (heliospectroscope, star spectroscope, telcspectroscope), 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 gravita- tion. 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 Scc- chi'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 iden- tity 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 "In- ternationale wissen.schaftliche Bibliothek" (Leipzig, 1878). Passing over his other investigations con- cerning comets, groups of stars, and nebulous stars, we may remark in pa-ssing that Schiaparelli's celebrated treati.se on the relations between the groups of aster- oids and comets wa-s pubH.shed in Secchi's "Bullet- tino meteorologico" (Rome, 1866).

As a meteorologist, Secchi was, as already said, an enthusiastic disciple of the American F. M. 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 quick- sand, 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 aa an eventual means of prognosticating the weather, and worke<l with good results in union with other observatories with similar aims (e. g. Greenwich, England). The .Magnetic Observatory, arranged and fitterl by Secchi in 1858, was for a long periofl the only one in Italy. Commissioned by Pius IX, who promoted all his undertakings with princely liberality, he ma^le long travels through France and Germany in 1858 t/) procure the most suitable pro- jection lenses for the hghthouses of the papal harbour

towns. He secured, however, his greatest fame by his invention of the "Meteorograph", a skilfully-con- structed weather machine, which works day and night and records the curves of atmospheric pre.ssure, temperature, rainfall, rainy season, strength of wind, and relative dampness of the atmosphere. In its original form the "Meteorograph" was ex- tremely 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 Exliibition of 1867. It created a great sensa- tion, 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. \n exact description of the ap- paratus with illustrations is given in the brochure, "II meteorografo del Collegio Romano" (Rome, 1870). As phy.sici.st 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 especi- ally deserves honourable mention. By discharging this tedioas 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 Ba.se trigono- metrica eseguita suUa Via Appia" (Rome, 1858). He acquired world-wide fame as a physicist by his greatly-admired work, "Sulla unit^ delle forze fisiche" (Rome, 1864), which attempts to trace all natural processes to kinetic energy. With astound- ing acumen he here combines in a uniform pic- ture 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, Engli.sh, German, and Ru.ssian. Secchi was, how- ever, 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 intel- lectual. 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. Guttler (Leipzig, 1882; 4th cd., 1885), ho gave a more than eloquent expression to his Chris- tian vi(!W 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 exp(l him from his laboratory, and he continued his investigations vmtil he succumbed to a fatal disorder of the stomach.

MoiOMO, P. Hecr.hi, sa vie, son obHervatoire, ses travaui, se.i (critH (Paris, 1879); Respiohi, Elogio del P. Secchi (Rome, 1879); Manuei.li, Sulln vita e le Opere del P. Secchi (Reggio, 18S1) : and in connexion therowith CiviUA Caltolicn, .scrips XL. vol. VII (Rome, 1881), .W) sqq.; Bricarei-li, Delia, vita e delle opere del P. Secchi (Rome, 1888); Millosevich, Commemorazione del P. Secchi