The Penumbra is the portion of the earth's surface that is partially shaded in the case of a total eclipse of the sun. (L. pene, almost.)
Note.—The diameter of the penumbra may vary slightly, but is usually about 4000 miles.
The Attributes of Darkness.
Darkness seems to be of a black color. The reason of this is, that, according to the theory of colors, blackness is owing to the non-reflection of light from the surfaces of bodies; and consequently, where no light exists to be reflected, nothing but seeming blackness can meet the eye.
When we speak of a deep gloom, we refer to the apparent, color of the gloom, as closely approximating to perfect blackness, deep being an epithet which, when applied to color, denotes intensity.
When we speak of darkness as being profound, we present the idea of local depth, as that of a fathomless pit.
When we speak of darkness as being thick, or gross, we represent it as a dark-colored fluid of great density.
When we speak of the sun's dispelling, dispersing, or scattering darkness, we represent it as something analagous to a fog or mist which is brushed away by the rising breeze.
When we speak of darknes as hovering or brooding over a scene, we represent it under the figure of a huge dark-colored fowl overshadowing the scene with its expanded wings.
Egyptian darkness is a figurative expression, denoting the utter absence of moral illumination among a people. The allusion is to the darkness which, in the time of Moses, covered the land of Egypt for the space of three days.
Cimmerian darkness is such as was represented by the ancients as perpetually involving the region of Cimmeria, (now Crimea.)
Sink and disperse, ye specter doubts that roll Cimmerian darkness on the parting soul. Campbell.
OF COLOR.
1. The Theory of Colors.
The light of the sun is naturally white; but by means of a piece of glass in the form of a triangular prism, the white light of the sun can be decomposed into seven different kinds of colored rays; namely, red, orange, yellow, green, blue, indigo, and violet. These, according to Newton, are the primary colors, and all other colors and shades of color may be produced by combining these primary colors in due proportions.
Some recent philosophers, however, hold that there are but three primary colors; namely, red, yellow, and blue; for orange can be produced by combining red and yellow; green, by combining yellow and blue; violet, by combining red and blue; and indigo is regarded as being but a modification of blue.
Bodies have in themselves, no color whatever; but their apparent color depends upon the color of the rays which they reflect. If a body reflect all the rays of solar light, its color will seem to be white. If the body absorb all the rays and reflect none, its seeming color will be black. White is, therefore, the union, in due proportion, of all the primary colors, and black is the absence of all. If a body absorb all the rays of sunlight except the red, and reflect the latter, the seeming color of the body will be red. If the yellow rays alone be reflected, the body will seem to be yellow. If the red and the yellow rays be both reflected, while the rest are absorbed, the resulting color will be orange, which is, as stated above, a combination of red and yellow.
The Prismatic Colors are those into which white light is decomposed by means of the prism.
A Hue is some specific color.
A Shade is a degree of any color.
A Cast, Tinge, or Tincture is a slight degree of some color.
A Tint is a slight superadded coloring distinct from the GROUND, or principal color.
2. The various designations of Color.
White is the combination of all the prismatic colors.
Hoar, white; as, hoar frost.
Hoary, white; as, hoary hairs.
Candeo, to be white. (L.) Hence
Candent, white with heat.
Candy, primarily and properly, refined sugar, from its whiteness.
Candor, a disposition to treat subjects with fairness, this disposition from its peculiar excellence, having been called by a name which signifies pure whiteness.
Candidate, an applicant for office, so called, because in Ancient Rome aspirants for public offices were arrayed in white garments.
Incandescence, a glowing whiteness caused by intense heat.
Blanc, white. (Fr.) Hence,
