The notions of the penumbra and umbra are important in considering eclipses (q.v.).
The umbra in the former case becomes the fully illuminated portion, and vice versa.
Each spot shows with more or less completeness a ring-shaped penumbra enclosing a darker umbra; the umbra, which looks black beside' the photosphere, is actually about as brilliant as limelight.
The umbra of a spot is generally not tormented by rapid line-of-sight motions; where any motion has been found G.
Marcion, for example, regarded the body of Christ merely as an "umbra," a "phantasms."
The true shadow or umbra, and also a definite boundary of the parts wholly illuminated.
The largest spots are easily seen by the naked eye, if the brilliancy of the disk is veiled; the umbra may be many - ten or more - diameters of the earth in breadth.
Some lines of certain elements are always seen fainter or thinner than on the photosphere, or even wholly obliterated; others sometimes show the same features, but not always; other lines of the same elements, perhaps originating at a level above the spot, are not affected; there are also bright streaks where even the general absorption of the spot is absent, and sometimes such a bright line will correspond to a dark line on the photosphere; most generally the lines are intensified, generally in breadth, sometimes in darkness, sometimes in both together, sometimes in one at the expense of the other; certain lines not seen in the photosphere show only across the umbra, others cross umbra and penumbra, others reach a short distance over the photosphere.
His attitude about this time to life and experience is reflected in Pulvis et umbra, one of the noblest of all his essays.
Sombre, gloomy, possibly from sub umbra, beneath the shade, is given as a parallel.
Readers of Dante know the idea that the dead have no shadows; this was no invention of the poet's but a piece of traditionary lore; at the present day among the Basutos it is held that a man walking by the brink of a river may lose his life if his shadow falls on the water, for a crocodile may seize it and draw him in; in Tasmania, North and South America and classical Europe is found the conception that the soul - o-tab., umbra - is somehow identical with the shadow of a man.
About the same time Francesco Maurolico, or Maurolycus, the eminent mathematician of Messina, in his Theore y nata de Lumine et Umbra, written in 1521, fully investigated the optical problems connected with vision and the passage of rays of light through small apertures with and without lenses, and made great advances in this direction over his predecessors.
NOCERA UMBRA (anc. Nuceria Camellaria), a town and episcopal see in the province of Perugia, Italy, 12 M.
A, B, C, D, F, Successub -umbra l sive stages in vercavity.
John Fleischer (sometimes incorrectly named Fletcher), of Breslau, propounded the same view in a pamphlet, De iridibus doctrina Aristotelis et Vitellonis (1574) the same explanation was given by Franciscus Maurolycus in his Photismi de lumine et umbra (1575) The most valuable of all the earlier contributions to the scientific explanation of rainbows is undoubtedly a treatise by Marco Antonio de Dominis (1566-1624), archbishop of Spalatro.