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    "source_title": "Encyclopaedia Britannica (1911)",
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    "verified_text": "janssen, pierre jules cesar (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 lycee 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.",
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