3. Relations of Bodies to Light.
Transparent bodies permit light to pass so freely, that objects beyond may be plainly seen. (L., trans, through; and pareo, to appear.)
Opake bodies are such as do not permit light to pass. A pane of window glass is transparent, but a board is opake.
Opacity (from opake) signifies a want of transparency. Blindness is sometimes caused by an opacity of the lens of the eye.
Opake also signifies not self-luminous. The sun is self-luminous, but the moon is an opake body. (L., opacus, shady.)
Clear. When bodies which are expected to be transparent are free from foreign matters, discolorations, and whatever else may tend to impair their transparency, they are said to be clear, as the air when free from mist, smoke, or dust; and water, when free from impurities.
Pellucid, perfectly transparent. (Pel for per, through; and luceo, to shine.)
Limpid, transparent. (Spoken only of liquids; as, a limpid stream.)
Semi-transparent, imperfectly transparent. (Semi, half.)
Translucent, permitting light to pass, but not so freely that objects beyond can be seen. (L., trans, through; and luceo, to shine.)
Diaphanous, transparent. (Gr., δια [dia] through; and φαινω [phaino], to shine.)
Crystal, resembling in transparency the mineral bodies called crystals; as a crystal fountain.
4. Of Darkness.
DARKNESS is the absence of light. In a figurative sense darkness is the absence of intellectual or spiritual light.
Dusk is a partial darkness. The dusk of the evening is the evening twilight.
Gloom is darkness, either partial or total; as, the gloom of a dense forest; the gloom of midnight.
Gloom, in a fig. sense, as denoting a state of the mind, is an absence of cheerfulness.
Murk is darkness.
Ere twice in murk and occidental damp,
Moist Hesperus hath quenched his sleepy lamp.—Shaks.
Murky, dark.
A murky storm, deep, low'ring o'er our heads,
Hung imminent, that, with imperious gloom,
Opposed itself to Cynthia's silver ray.—Addison.
Obscure, wanting light to such a degree, that objects can not be plainly discerned. Hence, fig. 1. Not easily understood; as, an obscure subject. 2. Not noted; as, an obscure person.
Sombre, gloomy; as, a sombre day. (Sp. sombra, a shade, from L. umbra.)
Shade consists in an absence of light caused by the interposition of an opake body between a surface, or empty space, and the source of light.
A Shadow is a shade with a definite outline delineated on a surface, the outline corresponding in form to the figure of the body which projects the shadow.
Umbra, a shade or shadow. (L.) Hence,
Umbrageous, shady; as, an umbrageous forest.
Umbrella, lit, a little shade. Hence a screen held in the hand as a protection against the sun or rain.
Umbrage. 1. Shade: <poem>
Men, sweltering, run To grots and caves, and the cool umbrage seek Of woven arborets.—Philips.
2. Shadow or appearance. The opinion carries no show of truth nor umbrage of reason on its side.—Woodward.
3. Offense taken at a procedure which we suspect as being designed to operate to our disadvantage.
Note 1.—Until the suspicion becomes a certainty, it is a mere umbra or shade.
Note 2.—Another explanation of the figure implied in the use of the word umbrage, in the sense of offense, is, that the cause of the offense casts a shadow over the mind of the offended party.
The Umbra is the dark spot on the earth's surface in the case of a total eclipse of the sun.
