JANSSEN, JOHANNES (1820-1891), German historian, was born at Xanten on the 10th of April 1829, and was educated as a Roman Catholic at Münster, Louvain, Bonn and Berlin, afterwards becoming a teacher of history at Frankfort-on-the-Main. He was ordained priest in 1860; became a member of the Prussian Chamber of Deputies in 1875; and in 1880 was made domestic prelate to the pope and apostolic pronotary. He died at Frankfort on the 24th of December 1891. Janssen was a stout champion of the Ultramontane party in the Roman Catholic Church. His great work is his Geschichte des deutschen Volkes seit dem Ausgang des Mittelalters (8 vols., Freiburg, 1878-1894). In this book he shows himself very hostile to the Reformation, and attempts to prove that the Protestants were responsible for the general unrest in Germany during the 16th and 17th centuries. The author’s partisanship led to some controversy, and Janssen wrote An meine Kritiker (Freiburg, 1882) and Ein zweites Wort an meine Kritiker (Freiburg, 1883) in reply to the Janssens Geschichte des deutschen Volkes (Munich, 1883) of M. Lenz, and other criticisms.
The Geschichte, which has passed through numerous editions, has been continued and improved by Ludwig Pastor, and the greater part of it has been translated into English by M. A. Mitchell and A. M. Christie (London, 1896, fol.). Of his other works perhaps the most important are: the editing of Frankfurts Reichskorrespondenz, 1376-1519 (Freiburg, 1863-1872); and of the Leben, Briefe und kleinere Schriften of his friend J. F. Böhmer (Leipzig, 1868); a monograph, Schiller als Historiker (Freiburg, 1863); and Zeit- und Lebensbilder (Freiburg, 1875).
See L. Pastor, Johannes Janssen (Freiburg, 1893); F. Meister, Erinnerung an Johannes Janssen (Frankfort, 1896); Schwann, Johannes Janssen und die Geschichte der deutschen Reformation (Munich, 1892).
JANSSEN, PIERRE JULES CÉSAR (1824-1907), French astronomer, was born in Paris on the 22nd of February 1824, and studied mathematics and physics at the faculty of sciences. He taught at the lycée Charlemagne in 1853, and in the school of architecture 1865-1871, but his energies were mainly devoted to various scientific missions entrusted to him. Thus in 1857 he went to Peru in order to determine the magnetic equator; in 1861-1862 and 1864, he studied telluric absorption in the solar spectrum in Italy and Switzerland; in 1867 he carried out optical and magnetic experiments at the Azores; he successfully observed both transits of Venus, that of 1874 in Japan, that of 1882 at Oran in Algeria; and he took part in a long series of solar eclipse-expeditions, e.g. to Trani (1867), Guntoor (1868), Algiers (1870), Siam (1875), the Caroline Islands (1883), and to Alcosebre in Spain (1905). To see the eclipse of 1870 he escaped from besieged Paris in a balloon. At the great Indian eclipse of 1868 he demonstrated the gaseous nature of the red prominences, and devised a method of observing them under ordinary daylight conditions. One main purpose of his spectroscopic inquiries was to answer the question whether the sun contains oxygen or not. An indispensable preliminary was the virtual elimination of oxygen-absorption in the earth’s atmosphere, and his bold project of establishing an observatory on the top of Mont Blanc was prompted by a perception of the advantages to be gained by reducing the thickness of air through which observations have to be made. This observatory, the foundations of which were fixed in the snow that appears to cover the summit to a depth of ten metres, was built in September 1893, and Janssen, in spite of his sixty-nine years, made the ascent and spent four days taking observations. In 1875 he was appointed director of the new astrophysical observatory established by the French government at Meudon, and set on foot there in 1876 the remarkable series of solar photographs collected in his great Atlas de photographies solaires (1904). The first volume of the Annales de l’observatoire de Meudon was published by him in 1896. He died at Paris on the 23rd of December 1907.
See A. M. Clerke, Hist. of Astr. during the 19th Century (1903); H. Macpherson, Astronomers of To-Day (1905).
JANSSENS (or Jansens), VICTOR HONORIUS (1664-1739), Flemish painter, was born at Brussels. After seven years in the studio of an obscure painter named Volders, he spent four years in the household of the duke of Holstein. The next eleven years Janssens passed in Rome, where he took eager advantage of all the aids to artistic study, and formed an intimacy with Tempesta, in whose landscapes he frequently inserted figures. Rising into popularity, he painted a large number of cabinet historical scenes; but, on his return to Brussels, the claims of his increasing family restricted him almost entirely to the larger and more lucrative size of picture, of which very many of the churches and palaces of the Netherlands contain examples. In 1718 Janssens was invited to Vienna, where he stayed three years, and was made painter to the emperor. The statement that he visited England is based only upon the fact that certain fashionable interiors of the time in that country have been attributed to him. Janssen’s colouring was good, his touch delicate and his taste refined.
JANSSENS (or Jansens) VAN NUYSSEN, ABRAHAM (1567-1632), Flemish painter, was born at Antwerp in 1567. He studied under Jan Snellinck, was a “master” in 1602, and in 1607 was dean of the master-painters. Till the appearance of Rubens he was considered perhaps the best historical painter of his time. The styles of the two artists are not unlike. In correctness of drawing Janssens excelled his great contemporary; in bold composition and in treatment of the nude he equalled him; but in faculty of colour and in general freedom of disposition and touch he fell far short. A master of chiaroscuro, he gratified his taste for strong contrasts of light and shade in his torchlights and similar effects. Good examples of this master are to be seen in the Antwerp museum and the Vienna gallery. The stories of his jealousy of Rubens and of his dissolute life are quite unfounded. He died at Antwerp in 1632.